REESE  LIBRARY 

OK  THK 

UNIVERSITY  OF  CALIFORNIA. 


,190 
on  No.     82893     •   Class  A 


POWER  DISTRIBUTION 


FOR 


ELECTRIC  RAILROADS 


BY 


LOUIS  BELL,   PH.D. 


THIRD   EDITION.     REVISED  AND   ENLARGED 


NEW  YORK  : 

STREET  RAILWAY  PUBLISHING  COMPANY 
1 20  LIBERTY  STREET 


COPYRIGHTj   1900. 

BY   THE 

STREET    RAILWAY    PUBUSHING    COMPANY, 
NEW  YORK. 


PREFACE. 


This  little  book  is  written  in  the  hope  that  it  may  be 
of  service  to  those  whose  daily  work  is  concerned  with 
the  art  of  transportation,  in  which  electrical  traction  is 
to-day  so  potent  a  factor.  The  part  it  may  play  to-morrow 
only  the  prophet  can  say. 

The  author  has  endeavored  to  set  forth  the  general 
principles  of  the  distribution  of  electrical  energy  to  mov- 
ing motors,  to  describe  the  methods  which  experience  has 
shown  to  be  desirable  in  such  work,  and  to  point  out  the 
ways  in  which  these  principles  and  methods  can  be  co-or- 
dinated in  everyday  practice.  The  art  of  correctly  design- 
ing systems  of  distribution  requires,  more  than  anything 
else,  skilled  judgment  and  infinite  finesse-,  it  cannot  be 
reduced  to  formulae  in  which  these  terms  do  not  enter  as 
variables.  The  most  that  can  be  done  is  to  sketch  the 
lines  of  thought  that,  followed  cautiously  and  shrewdly, 
lead  to  good  results. 

For  the  most  part  apparatus  is  too  mutable  to  describe 
exhaustively,  unless  one  is  writing  history.  The  reader 
will  therefore  find  little  of  such  detail,  save  in  the  frontier 
region  which  lies  between  established  tramway  practice 
and  that  greater  field  that  stretches  toward  unknown 
bounds.  Along  that  frontier  experiment  has  blazed  paths 
here  and  there,  and  we  must  note  them  carefully.  We 
can  see  whither  they  lead,  but  dare  not  say  how  far. 

The  best  advice  that  can  be  given  to  the  engineer  is 
to  keep  his  eyes  and  ears  open  and  never  to  let  himself  get 
caught  out  of  sight  of  experimental  facts. 


82893 


PREFACE  TO  THE   THIRD   EDITION. 


The  past  three  years  have  been  marked  by  nothing 
particularly  startling  in  the  way  of  innovations.  Electric 
railways  are  more  numerous  and  longer,  and  apparatus  is 
on  a  bigger  scale  now  than  then,  but  the  changes  in ' 
methods  have  been  few  and  trifling.  The  most  notable 
line  of  growth  has  been  in  the  increasing  use  of  substa- 
tions with  rotary  converters,  sometimes  with  admirable 
results,  sometimes  with  more  energy  than  discretion.  Stor- 
age battery  auxiliaries  have  also  been  on  the  increase  with 
varying  economic  effect.  On  the  other  hand,  little  progress 
has  been  made  in  heavy  railway  work,  save  in  the  multi- 
plication of  roads,  and  the  problem  of  economical  distribu- 
tion for  such  work  has  not  advanced  toward  solution. 
The  substation  idea  has  not  yet  been  advanced  beyond  the 
crude  conception  of  substituting  motor  for  engine  in  an 
auxiliary  station  without  improvement  in  the  feeding 
system  of  the  motors.  This  volume  deals  with  principles 
and  methods,  and  consequently,  while  it  is  pleasing  to 
note  that  the  motor  has  practically  driven  the  locomotive 
off  elevated  roads,  that  third  rail  surface  traction  for  heavy 
service  is  on  the  increase,  and  that  long  distance  surbur- 
ban  roads  have  developed  with  splendid  rapidity,  one  must 
regretfully  admit  that  the  examples  of  each  given  in  the 
first  edition  are,  save  in  unimportant  details,  as  typical  of 
.current  practice  in  1900  as  they  were  in  1896.  Improve- 
ments d/e,  however,  already  overdue,  for  we  are  still  a  long 
way  from  the  filial  development  of  electric  traction. 


CONTENTS. 


CHAPTER  I. 

FUNDAMENTAL,   PRINCIPLES. 

Classes  of  distribution — Fundamental  formulae  of  distri- 
bution— Plate  I,  showing  size  of  conductors  for  various 
losses — Losses  with  distributed  and  moving  loads — Simple 
and  branched  lines — Irregular  distribution  of  loads — Center 
of  gravity  of  load — Location  of  centers  of  distribution — Net- 
works and  their  computation — Variations  of  load,  their 
nature  and  magnitude. 1-27 


CHAPTER  II. 
THE  RETURN  CIRCUIT. 

Nature  of  the  return  circuit — Conductivity  of  rails — 
Systems  of  bonding — Arrangement  of  bonds — Resistance  of 
bonds  and  bond  contacts — Earth  resistance — Leakage  of 
current  from  the  rails  to  earth  and  other  conductors-— Elec- 
trolysis, its  distribution  and  amount — Remedies — Supple- 
mentary wires — Continuous  track — Welded  and  cast  joints 
— The  double  trolley — Energy  lost  by  bad  bonding — Net  re- 
sistance of  bonded  track — Track  constants — Formula  for 
complete  circuit 28-59 


CHAPTER  III. 
DIRECT  FEEDING  SYSTEMS. 

Systems  of  arranging  feeders — Maximum  and  average 
drop — Load  factor  of  the  station — Wandering  load — Compu- 
tation of  a  feeder  system — Extent  of  lines — Average  load  «n 
lines — Center  of  distribution — Maximum  loads — Trolley 
wire  and  track  return — General  feeding  system — Reinforce- 
ment at  special  points — Plate  II,  chart  for  feeder  computa- 
tion— Cost  of  wasted  energy 60-87 


VI  CONTENTS. 

CHAPTER  IV. 

SPECIAL  METHODS  OF  DISTRIBUTION. 

Boosters,  their  proper  and  improper  use — Three  wire 
system — Methods  of  balancing — Self  contained  three  wire 
system — Advantage  of  high  voltage — Motors  in  series — In- 
crease of  working  voltage — Arrangement  of  feeders — Com- 
posite systems 88-108 

CHAPTER  V. 

SUBSTATIONS. 

Auxiliary  stations — Distributed  stations — Substations 
with  power  transmission — Cost  of  power  in  stations  of  vari- 
ous sizes — Single  station  vs.  distributed  stations — A  typical 
auxiliary  station — Conditions  of  economy — Typical  dis- 
tributed stations — Typical  transmission  station — Compari- 
son of  substation  methods — Relative  costs 109-143 

CHAPTER  VI. 
TRANSMISSION  OF  POWER  FOR  SUBSTATIONS. 

Generation  of  alternating  current — Modern  alternators 
— Necessity  of  high  voltage — Inner  pole  machines — Trans- 
formers —  Transmission  lines  —  Insulators  —  Synchronous 
motors — Polyphase  generators — Substations  with  synchro- 
nous motors — Motor  generators — Rotary  converters — Lag- 
ging and  leading  current — Computation  of  an  alternating 
line — of  a  three  phase  line — Operation  of  the  machines.  .  .  144-177 

CHAPTER  VII. 

ALTERNATING  MOTORS  FOR  RAILWAY  WORK. 

Varieties  of  alternating  motors — Synchronous  motors 
with  commutating  start — with  inductive  start — Properties 
of  synchronous  motors — Polyphase  induction  motors — their 
structure  and  properties — Regulation  of  speed — Torque — 
Tests  of  polyphase  induction  motors  for  railway  service — 
their  weak  points — The  first  polyphase  railway — Induction 
motors  on  monophase  circuits — Methods  of  working  poly- 
phase motors  from  monophase  circuits — Monophase  induc- 
tion motors  and  their  properties — Application  of  alternating 
transmission  to  railway  work — Its  economic  relation  to 
other  methods  of  working .' 178-220 


CONTENTS.  Vll 

CHAPTER  VIII. 
INTERURBAN  AND  CROSS  COUNTRY  WORK. 

Conditions  on  interurban  roads — Power  required — Com- 
putation of  the  feeding  system — Economy  of  various 
methods  of  distribution — Light  electric  roads  for  country 
districts — Narrow  gauge  roads-cost  of  construction  and  op- 
eration— Bicycle  and  saddle-back  roads-cost  of  construction 
and  operation 221-250 

CHAPTER  IX. 

FAST  AND   HEAVY  RAILWAY  SERVICE. 

Kinds  of  work  for  which  electric  power  is  best  suited — 
Suburban  passenger  traffic — Conditions  of  competition  be- 
tween steam  and  electricity — Power  required  for  operating 
electrically — Special  trolley  systems — Computation  of  the 
feeders — Cost  of  overhead  system — The  third  rail  system — 
The  Nantasket  road — Cost  of  electric  power  for  suburban 
work — Very  high  speeds — Air  resistance — Other  resistances 
— Tractive  power  required — Track  for  extreme  speeds — 
Methods  of  operation — The  braking  problem — Computation 
of  the  feeding  system — Cost  of  power — Electric  elevated 
roads — The  Metropolitan  road  of  Chicago — The  Lake  Street 
road  of  Chicago.  Distribution  of  the  power — Special  heavy 
service — The  Baltimore  &  Ohio  tunnel — Results  already  at- 
tained— Electric  passenger  locomotive — Methods  of  power 
distribution 251-303 


CHAPTER  I. 

FUNDAMENTAL,   PRINCIPLES. 

The  distribution  of  electrical  energy  for  use  in  propel- 
ling railway  cars  is,  by  nature,  a  special  problem.  It  deals 
with  magnitudes  and  distances  greater  than  are  usual  in 
other  branches  of  electrical  engineering,  and,  in  addition, 
with  the  difficulties  of  a  load  that  constantly  shifts  in 
amount  and  position.  Consequently,  the  design  of  a  dis- 
tributing system  is  of  singular  difficulty. 

In  computing  the  area  of  conductors,  one  ordinarily 
assumes  the  load  to  be  the  only  independent  variable,  but 
in  this  case  the  distance  of  transmission  must  be  so  consid- 
ered, and  both  quantities  are  of  the  most  erratic  character. 

The  general  equations  can  therefore  only  be  solved 
within  limits,  except  in  special  cases,  and  even  then  only 
by  very  judicious  assumptions.  It  is  therefore  worth  while 
to  investigate  these  limits,  their  extent  and  the  causes 
which  impose  them. 

The  conducting  system  of  an  electric  railway,  large  or 
small,  consists  of  three  somewhat  distinct  parts — the  work- 
ing conductor,  the  return  circuit  and  the  feeders.  By  the 
first  is  meant  that  part  of  the  total  circuit  from  which  the 
moving  contact,  carried  by  the  car,  immediately  derives  its 
current.  Physically  it  is  a  wire  or  bar,  uninsulated  as  re- 
spects the  moving  contact,  and  supported  in  any  position — 
overhead,  on  the  ground  or  under  the  ground — that  cir- 
cumstances may  require. 

The  return  circuit  is,  in  a  large  proportion  of  cases, 
that  which  receives  current  from  the  wheels  of  the  car,  and 
is  composed,  partly  or  wholly,  of  the  rails.  In  certain 
cases,  conduit  roads,  double  trolley  roads  and  telpher  sys- 
tems, the  working  and  return  conductors  are  alike  and  of 


2        POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

equal  resistance.  They  may  therefore  be  treated  alike  as 
parts  of  the  working  circuit.  The  ordinary  return  circuit 
calls  for  special  investigation,  because  it  is  a  heterogeneous 
conductor,  unequal  in  resistance  to  the  working  conductor, 
and  involving  unusual  complications. 

The  feeding  system  in  railway  work  serves  the  double 
purpose  of  reinforcing  the  conductiyity  of  the  working  con- 


FIG.  i. 

ductor  and  equalizing  the  voltage  at  various  parts  of  the 
system.  It  therefore  must  be  deferred  as  a  practical  matter 
until  the  working  system,  which  it  supplements,  has  been 
considered. 

Three  classes  of  working  systems  are  common,  making 
the  classification  according  to  the  nature  of  the  distribution. 


ID 

FIG.   2. 


The  first  class  is  illustrated  by  the  linear  system,  shown 
in  Fig.  i.  Ideally  it  is  a  straight  line,  A  B,  near  some 
point  at  which  the  power  station  is  generally  situated.  It 
may  be  modified  by  bends  or  curves,  as  in  A1"Bl  and 


FUNDAMENTAL,    PRINCIPLES. 


A2B3 ,  but  whether  it  be  a  small  tramway  line  along  a  single 
street,  or  a  long  interurban  road,  it  retains  as  its  main 
characteristic  a  single  working  line,  not  generally  re-curved 
on  itself,  and  subject  throughout  its  length  to  fairly  uni- 
form conditions  of  traffic. 

The  second  class  is  illustrated  by  the  branched  type, 
represented  in  Fig.  2.  As  shown,  it  consists  of  a  main 
line,  A  B,  into  which  run  two  branches,  C  D  and  K  F. 
The  branched  distribution  is  the  one  most  commonly  met 
with  in  electric  street  railways  of  moderate  size,  and  may 
assume  an  infinite  variety  of  forms.  It  is  the  legitimate  re- 


suit  of  growth  from  the  linear  type,  and,  through  all  its 
modifications,  is  noteworthy  in  consisting  of  several  lines 
which  are  neither  interlinked,  although  often  overlapping, 
nor  subject  to  the  same  traffic  conditions.  Its  conducting 
system  is  therefore  essentially  complex. 

Finally,  we  have  the  meshed  system,  Fig.  3.  Ideally, 
it  is,  as  shown,  a  simple  network  composed  of  parallel  lines 
crossing  each  other  at  right  angles  and  at  nearly  equal  in- 
tervals, and  under  fairly  uniform  conditions.  Practically, 
the  various  lines  composing  the  network  cross  at  all  sorts  of 
angles  and  intervals,  and  are  subject  to  all  sorts  of  condi- 
tions of  traffic.  All  networks  however  have  this  property, 
tnat  they  are  composed  of  interconnected  lines,  so  that  the 
conducting  system  of  any  line  can  reinforce,  andean  be- re- 
inforced by,  other  systems.  Fig.  4  shows  that  portion  of 


4     POWER   DISTRIBUTION  FOR   ELECTRIC   RAILROADS. 


the  Boston  network  which  lies  within  a  mile  radius  from 
the  Post  Office  as  a  center.  It  conveys  an  idea,  better  than 
any  words,  of  the  sort  'of  network  that  occurs  in  practice. 
It  differs  totally  from  the  networks  usually  met  with  in  elec- 
tric lighting,  in  that  it  is  without  any  pretense  of  sym- 
metry, either  in  configuration  or  load. 

In  all  large  installations  one  is  likely  to  find  all  three 
types  of  distribution,  usually  a  network  in  the  center,  and 
branched  and  linear  distribution  in  the  outlying  districts. 
In  laying  out  the  system  as  a  whole,  each  type  must  con- 
form, as  far  as  practicable,  to  its  own  conditions  of  economy, 

while  the  general  feeding 
system  must  consider 
them  all. 

The  starting  point  in 
any  discussion  of  a*  con- 
ducting system  for  any 
purpose  is  Ohm's  law  in 
its  simplest  form 


C=- 


R 


FIG.  4. 


In  problems  of  distri- 
bution such  as  we  are 
considering,  the  term  in- 
volving R  is  usually  the 
quantity  sought,  since 

the  current  and  loss  of  potential  are  generally  known 
or  assumed.  It  is  therefore  desirable  to  transform  this 
simple  equation  into  some  form  which  allows  the  ready 
substitution  of  the  known  quantities  to  determine  the  un- 
known. The  resistance  of  any  conductor  may  be  written 

R  =  K-^-,    in  which  A  is  the  cross  section,  L  the  length 
A 

and  K  a  constant  depending  on  the  material  considered  and 
the  units  in  which  L  and  A  are  measured.  If  L  is  in  feet 
and  A  in  square  inches  the  constant  is  obviously  different 
from  what  it  would  be  if  I,  were  taken  in  miles.  The  con- 
stant is,  in  practice,  so  taken  that  R  will  be  in  ohms  when 


FUNDAMENTAL   PRINCIPLES. 

I,  ?.nd  A  are  in  convenient  units.  In  English-speaking 
countries  it  is  usual  to  take  L  in  feet  and  A  in  circular 
mils,  i.e.,  circles  ToVo  of  atl  incn  'm  diameter.  The  con- 
stant connecting  L,  in  feet  and  A  in  circular  mils  with  the 
resistance  in  ohms,  for  copper  wire  of  ordinary  quality  at 
ordinary  temperatures,  is  u.  This  is  approximately  the 
resistance  in  ohms  of  a  commercial  copper  wire  one  foot 
long  and  yoVir  °f  an  incn  *n  diameter.  The  exact  figure  is 
a  trifle  less,  but  the  ordinary  contingencies  of  temperature, 
joints,  etc.  ,  make  it  desirable  to  take  1  1. 

Substituting  now  this  value  of  R  in  Ohm's  law  it  be- 
comes, reckoning  the  area  in  circular  mils, 

Tf 

C  =  -  —  —  or,  transposing, 


c.m. 

nCL 
(i)    c.m=      —    — 


This  is  the  fundamental  equation  of  electrical  distribu- 
tion. It  is  like  the  original  form  of  Ohm's  law,  strictly  a 
linear  equation,  so  that  all  the  quantities  are  connected  by 
simple  proportions.  Doubling  K,  for  example,  halves  c.m.y 
while  doubling  I,  doubles  c.m.  A  convenient  transposed 
form  is 


II  ly 

which  determines  the  current  which  a  particular  line  will 
carry  without  exceeding  a  given  loss,  and  another, 

(3)E«=2i£k 

c.m. 

is  convenient  in  figuring  the  actual  fall  of  voltage. 
Throughout  these  equations  K  represents  the  fall  in  volts 
through  the  conductor  under  consideration,  and  I/  is  al- 
ways the  total  length  of  the  wire,  i.e.,  double  the  length  of 
the  circuit,  assuming  a  uniform  return  wire.  For  grounded 
circuits  the  equations  give  correct  results  for  so  much  of  the 
circuit  as  is  exclusively  copper — the  grounded  portion  in- 
volves a  different  constant  and  must  be  taken  up  as  a  sep- 
arate problem. 


6       POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

It  is  often  convenient  to  have  some  simple  expression 
connecting  the  area  of  a  wire  with  its  wt  ight,  so  that  the 
latter  may  be  readily  taken  into  account.  By  a  fortunate 
chance,  a  copper  wire,  1000  c.  m.  in  section  weighs  almost 
exactly  three  pounds  per  1000  ft.  So  if,  in  equation  (i), 
we  multiply  the  constant  by  three,  and  reckon  L,  in  thous- 
ands of  feet,  we  obtain  directly  the  weight  of  conductor  per 
1000  ft.  Putting  Lm  for  the  length,  to  distinguish  it  from 
the  former  I,  reckoned  in  feet,  we  have 

(4)  Wm=3 


Thus,  if  we  wish  to  transmit  100  amperes  through  7000 
ft.  of  conductor  at  a  loss  of  50  volts,  the  conductor  must 

weigh  33°°X  7=462  Ibs.  per  1,000  ft.      The  total  weight 

50 

of  conductor  is  evidently  Wm  I,m  ,  and  since  a  simple  way 
of  getting  the  total  weight,  without  reference  to  wire 
tables,  is  often  desirable,  we  may  re-  write  (4),  as  follows: 


which  gives  the  total  weight  directly.  These  weight  form- 
ulae are  very  easy  to  remember  and  apply,  and  are  accurate 
to  about  one  per  cent. 

The  diagrams  of  Plate  I.  put  equations  (i),  (3),  (4) 
in  graphic  form  for  ready  reference.  Four  different 
values  of  K  are  assumed,  and  the  unit  of  power  is  taken 
as  100  amperes.  The  chart  is  therefore  independent  of 
the  initial  pressure,  and  serves  for  transmission  at  any 
ordinary  voltage.  Distances  on  the  horizontal  axis  repre- 
sent length  of  circuit,  i.  e.  ,  half  the  total  length  of  con- 
ductor. To  find  area  or  weight  per  1000  ft.  of  conductor 
required  for  a  certain  distance,  take  an  ordinate  at  the  re- 
quired point  on  the  distance  scale  and  follow  it  up  until 
it  intersects  the  oblique  line  representing  the  assumed  loss 
of  voltage.  The  area  of  the  necessary  wire  can  then  be 
read  off  on  the  left  hand  scale,  and  the  weight  per  1000  ft. 
on  the  right.  The  corresponding  sizes  of  the  B.  &  S. 
gauge  wires  are  annexed  to  the  former  scale.  In  a  similar 


FUNDAMENTAL   PRINCIPLES. 


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20                                25 
Street  Railway  Journal 

8       POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

way  the  distance  for  which  a  given  wire  will  carry  100 
amperes  at  a  given  loss  can  be  found,  while  the  loss  for  a 
given  wire  and  distance  can  be  rapidly  approximated  by 
estimating  the  position  of  the  intersection  of  the  area  and 
the  distance  co-ordinates  with  reference  to  the  oblique 
lines.  By  noting  that  the  area  of  conductor  varies  inverse- 
ly with  K,  one  can  extend  the  working  range  of  the  chart. 
Halving  the  area  shown  for  B  =  75  gives,  for  instance, 
the  area  for  K  =  150,  and  so  on. 

Taking  up  now  the  case  of  linear  distribution,  it  has 
already  been  shown  that  the  fall  in  voltage  in  any  con- 
ductor is  directly  proportional  to  the  load  and  the  resist- 
ance. If,  now,  a  uniform  line,  A  B,  Fig.  5,  be  loaded  at 
B,  the  voltage  evidently  decreases  uniformly  throughout 
its  length.  To  make  the  example  more  concrete,  the 
length  A  B  is  taken  as  20,000  ft.,  and  the  voltage  kept 
constant  at  A,  e.  g. ,  500.  Now,  if  the  drop  at  B  under  the 
given  load  be  100  volts,  a  straight  line  drawn  from  C  to  D 
shows  the  state  of  the  voltage  at  every  point  of  the  line. 
An  ordinate  erected  at  any  point  of  A  B  and  extended  to 
C  D  shows  the  voltage  of  the  line  at  the  point  selected,  and 
that  part  of  the  extended  ordinate  cut  off  between  C  D  and 
C  F  shows  the  loss  in  volts.  If  the  load  be  transferred 
from  B  to  some  intermediate  point  of  the  line,  an  ordinate 
there  erected  will  show  the  drop  and  the  residual  voltage 
at  the  new  point.  C  K  similarly  shows  the  conditions  for 
a  terminal  drop  of  200  volts. 

The  average  drop  is  evidently  half  .the  maximum  in 
each  case,  since  the  minimum  drop  is  o,  and  the  voltage 
varies  uniformly. 

Now  suppose  one  has  to  deal  with  a  load  moving  uni- 
formly back  and  forth  along  A  B.  If  the  maximum  drop 
be  i  oo  volts,  the  voltage  evidently  moves  uniformly  along 
C  D,  and  the  average  voltage  is  450,  since  half  the  time 
the  voltage  is  above  this,  and  the  other  half  an  exactly 
equal  amount  below. 

This  case  corresponds  to  a  line  traversed  on  a  uniform 
schedule  by  a  single  car.  Such  however  is  not  the  usual 


FUNDAMENTAL,  PRINCIPLES. 


condition  of  things.  The  normal  condition  of  an  electric 
road  of  any  kind  is  a  plurality  of  cars.  This  means  that 
current  is  taken  from  the  working  conductor  at  a  certain 
limited  number  of  points.  In  general,  these  points  repre- 
sent approximately  equal  loads  and,  so  long  as  the  time 
table  is  maintained,  are  approximately  equidistant.  In 
Fig.  6,  the  uniform  straight  conductor,  A  B,  is  loaded,  not, 


400 


2  300 


200 


100 


3  10  15 

Distances  — 1000  ft.  units. 


FIG.   5. 


Street  Ry.  Journal 


as  in  Fig.  5,  at  one  point,  but  at  ten  equidistant  points, 
the  loads  being  assumed  equal,  as  they  would  be  quite 
nearly  if  each  load  were  a  car  on  a  level  track. 

Here  the  conditions  of  fall  in  voltage  are  radically  dif- 
ferent from  the  conditions  of  Fig.  5.  At  the  power  sta- 
tion, A,  the  full  current  for  the  entire  load  is  supposed  to 
be  delivered  at  a  uniform  pressure  of  500  volts.  Assume 
the  total  current  to  be  200  amperes,  and  the  resistance  of 


10     POWER    DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 

each  of  the  uniform  sections  to  be  0.05  ohm.  The  first 
section  carries  the  whole  200  amperes,  and  the  drop  C  R  is 
10  volts.  The  second  section  carries  but  180  amperes,  and 
the  loss  is  9  volts,  and  so  on,  until  the  tenth  section  carries 
20  amperes,  and  the  loss  has  diminished  to  i  volt. 

Mapping  these  successive  falls  of  potential  on  Fig.  6, 
the  curved  line,  C  D,  is  formed,  showing  the  consecutive 


Points  on  line 


FIG.   6. 


9         10 
Street  Ry.  Journal 


values  of  the  potential  on  A  B.  C  E,  a  prolongation  of 
the  drop  in  the  first  section,  shows  the  result  of  concen- 
trating the  whole  load  at  B. 

In  such  a  uniformly  loaded  line  the  drop  is  found  as 

follows  :  If  C  is  the  total  current  and  there  are  n  sections 

P 
in  the  line,  then is  the  current  taken  off  for  each  sec- 

n 


FUNDAMENTAL   PRINCIPLES.  H 

p 

tion,  and  —  —  r  is  the   drop   due  to   that  current,  where  r 

is  the  resistance  of   each  section.     The  drop  in  the  first 

C  C 

section  from  A  is  10  -  r,  in  the  second   section  9  -  r 

n  n 

and  so  on  ;    i.  e.  ,  for  the  whole  n  sections  the  total  drop 
must  be 

(6)  E=-^r(i  +  2-j-3  .    .    .«) 
n 

But  the  sum  of  this  series  of  integers  is  well  known,  being 
—  -  -  -.     Hence,  substituting  and  reducing,  we  have 


2V 

This  gives  the  total  drop  produced  by  n  uniform  loads 
uniformly  spaced  and  aggregating  C  amperes. 

It  is  generally  convenient  to  have  working  formulae 
give  the  cross  section  of  conductor  directly,  since  that  is 
most  frequently  the  quantity  to  be  determined.  Equa- 
tion (3)  can  readily  be  transformed  for  this  purpose  as 
follows: 


c.  m. 

But  since  the  R  here  concerned  is  the  total  resistance, 
and  not  the  resistance  per  section  r,  as  in  (7),  we  may 
write, 

„  __      ii  L 


Then  substituting  this  value  of  rin  (7)  and  reducing,  we 
have 


2  \    n 

This  equation  gives  the  area  of  conductor  required  for  C 
amperes  supplying  a  line  of  known  length  equally  loaded 
at  n  points  at  any  required  terminal  drop. 

For  a  large  number  of  sections        n     r   I     approach- 
es unity,  so  that,  for  a  given  current  in  amperes  and  a 


12     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

given  terminal  drop,  the  copper  necessary  for  a  uni- 
formly distributed  load  is  one-half  that  required  for  the 
same  load  concentrated  at  the  end  of  the  line.  As  the 
number  of  sections  increases,  too,  the  likelihood  of  ob- 
taining a  disarrangement  of  load  sufficient  to  disturb  the 
terminal  voltage  much,  decreases.  The  effect  of  a  uni- 
form motion  of  all  the  loads  on  the  terminal  voltage  is 
small.  So  long  as  the  schedule  is  uniform  and  is  ad- 
hered to,  the  worst  that  can  happen  is  a  transformation 
of  the  system  into  half  the  original  number  of  sections. 
Suppose  in  Fig.  6  all  the  load  points  of  odd  numbers  to 
be  moving  to  the  right  and  all  those  of  even  number  to 
the  left,  at  uniform  speed.  Then  after  each  point  had 
moved  half  a  section,  there  would  be  five  sections  each 
loaded  with  a  pair  of  coincident  loads.  Applying  (7)  to 
the  data  of  Fig.  6,  K  =  60,  assuming  the  sections  uniform. 
As,  however,  the  first  section  would  be  but  three-  fourths 
the  length  of  the  others,  the  real  loss  would  be  55  as 
before.  Another  equal  movement  and  the  ten  sections  ap- 
pear in  their  original  relation.  Another  and  we  have  the 
five  sections,  but  with  an  initial  section  one-fourth  the 
length  of  the  others  and  total  loss  of  45  volts.  Next 
would  come  a  ten-section  arrangement,  but  with  the  first 
load  at  A,  and  K  =  45,  and  so  on.  The  upshot  is  that 
while  the  terminal  voltage  oscillates  through  a  range  equal 
to  the  drop  in  the  first  section,  the  final  effect  on  the  aver- 
age drop  of  uniformly  moving  the  loads  is  the  same  as  load- 
ing each  section  at  the  middle  point  or  increasing  n  in- 
definitely. Hence,  in  a  line  with  uniformly  spaced  and  uni- 
formly moving  loads,  we  may  assume 

n+  *  1  =  i  in  (9)  and  write 


or,  transposing, 

L      ii  C 
c,m.=-.    _. 

That  is,  the  area  of  the  line  can  be  calculated  for  average 


FUNDAMENTAL   PRINCIPLES.  1$ 

terminal  drop  just  as  if  the  load  were  concentrated  at  its 
middle  point.  Hence,  for  all  practical  purposes,  by  making 
this  assumption,  equations  (i),  (4),  (5)  can  be  used  in 
calculating  the  line. 

To  keep  the  voltage  approximately  uniform  over  a 
linear  system  of  distribution  is  comparatively  easy.  In  the 
most  favorable  case,  a  number  of  uniform  loads  moving  uni- 
formly, the  drop  is  half  that  met  with  in  the  most  unfavor- 
able distortion  of  the  load,  z.  e. ,  bunching  at  the  end  of  the 
line.  This  latter  condition  brings  the  worst  possible  load 
upon  the  station,  barring  short  circuits.  Although  long 
stretches  of  uniform  conductor  often  occur  in  railway  prac- 
tice it  is  usual  to  reinforce  the  working  conductor  by  feed- 
ers variously  arranged,  as  will  be  shown  later.  Such  feed- 
ers were  very  necessary  in  the  early  days  when  trolley  wire 
as  small  as  No.  4  was  used,  but  now,  when  No.  oo  is  very 


FIG.  7. 

commonly  employed,  elaborate  feeding  systems  are  less 
necessary  for  linear  working.  The  most  important  linear 
distributions  are  likely  to  come  in  long  inter  urban  roads, 
which  often  demand  special  methods  of  feeding.  What- 
ever these  may  be,  the  uniform  working  conductor  is  of 
sufficient  importance  in  every  system  to  warrant  this  dis- 
cussion of  its  general  properties. 

As  a  corollary  to  this  general  investigation,  it  is  evi- 
dent that  in  dealing  with  any  linear  system  such  as  A  B, 
Fig.  6,  the  best  point  for  the  power  station  is  at  the  middle 
point  of  the  line,  since  under  the  conditions  of  uniform  load 
supposed,  this  point  would  give  the  smallest  average  drop. 
Since  Iy  in  such  case  is  one-half  of  its  value  when  the  whole 
line  is  fed  from  A,  the  total  copper  by  equation  (5)  is  re- 
duced to  one-fourth  the  amount  for  the  same  loss. 

Considering  now  the  branched  type  of  distribution, 
shown  in  Fig.  2,  it  is  best  to  take  it  up  in  the  simplest 
available  form.  This,  Fig.  7,  shows  a  main  line,  A  B  D, 


14    POWER  DISTRIBUTION  FOR  ELECTRIC   RAILROADS. 

with  a  branch,  B  C,  which  is  straightened  and  made  paral- 
lel to  the  main  in  order  to  more  clearly  show  their  rela- 
tions. Unless  the  branch  is  of  such  magnitude  and  posi- 
tion as  to  require  special  feeders,  it  is  supplied  with 
current  from  the  main  linear  system.  In  a  few  cases  the 
service  on  a  branch  is  from  B  to  C  and  back.  More  gen- 
erally it  is  from  C  to  A  and  back,  a  part  of  the  cars  being 
devoted  to  a  through  branch  route.  On  the  section  A  B, 
the  load  is  the  sum  of  those  due  to  each  line  of  cars.  Be- 
yond B  there  are  two  independent  linear  systems. 


If  there  are  m  cars  on  the  route  A  D,  and  n  cars  on 
the  route  A  C,  then  the  load  on  A  B,  due  to  both  lines, 
will  be 


and  the  loads  on  B  C  and  B  D  respectively  will  be 

nWc  B~D 

Z5 and  m  15' 

Consequently,  if  the  section  A  B  is  computed  for  this  load 
according  to  (10)  we  shall  get  the  proper  conductor  for  the 
assumed  loss  E.  The  lines  B  C  and  B  D  can  then  be  com- 
puted for  losses  Et  and  E3.  The  values  o£  E,  Ex,  E2  are 
usually  taken  with  the  condition  imposed  that  E+E^ 
B  +  E3  shall  be  less  than  a  certain  specified  maximum. 
A  more  general  method  is  that  of  Fig.  8.  Here  there  is  a 
line,  A  B,  with  branches  running  to  C,  D,  E,  F.  The 
loads  are  /,  m,  n,  o,  p,  amperes  respectively.  A  B,  A  C, 
A  D,  A  B,  A  F,  are  now  considered  as  separate,  each  subject 


FUNDAMENTAL    PRINCIPLES.  15 

to  its  own  conditions.  Taking  now  a  drop  for  each  line, 
according  to  the  dictates  of  economy  or  convenience,  and  fig- 
uring the  conductors  from  (  10)  with  the  respective  currents, 
an  area  is  found  for  the  conductor  belonging  to  each  line. 
Then  the  cross  section  of  copper  required  from  A  to  the 
first  branch  is  [c  m\  \  -f-  [c  m~]  m  -f-  .  .  .  .  That  from  the. 
first  to  the  second  branch  is  [c  m~\m-\-  \c  m~\n-\-  ..... 
and  so  on.  In  practice  the  conductors  would  be  installed 
«sof  the  nearest  convenient  size,  neglecting  small  variations 
of  B  from  the  calculated  amount  at  the  termini  of  the 
various  lines. 

The  same  procedure  applies  to  all  sorts  of  independent 
lines  radiating  and  fed  from  a  common  center,  whether  or 
not  these  lines  have  any  sections  in  common. 

s  We  have  thus  far  assumed  all  lines  to  be  uniformly 
loaded  all  along  their  lengths.     It,  of  ten  happens  how- 


•B 


£ 


c 
*IG.  9. 

ever  that  for  some  cause  a  line  is  loaded  unequally.  In 
the  long  run,  grades  partially  compensate  themselves, 
since  as  many  cars  run  down  by  gravity  as  go  up  by  the 
expenditure  of  extra  power,  so  that  their  effect  shows 
more  in  the  variations  of  power  required  than  in  the  total 
amount.  Not  infrequently,  howrever,  from  the  effect  of 
grades,  curves  or  local  cars  in  an  extended  system,  there 
is  a  regular  demand  for  extra  power  at  some  point  of  the 
line.  This  is  shown  in  Fig.  9.  Here  the  line,  A  B,  is 
divided  into  ten  sections,  each  equally  loaded,  except 
that  at  8  the  load  is  three  times  the  normal.  Now  it  has 
just  been  shown  that  a  uniformly  (distributed  load  is  the 
same  in  effect  as  if  it  were  concentrated  at  the  middle 
point  of  the  loaded  line;  that  is,  the  electrical  loads,  like 
mechanical  ones,  act  as  if  concentrated  at  their  center  of 


1 6     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

gravity.  Hence  we  may  represent  the  above  case  by 
A'  B',  Fig.  9.  If  c  be  ^the  normal  load  of  each  section, 
then  a  load  of  10  c  will  be  concentrated  at  C  while  a  load 
of  2  c  is  at  D.  Hence,  following  out  the  principle  of 
center  of  gravity,  the  system  requires  for  a  fixed  value  of 
terminal  drop  the  same  extra  area  of  copper  as  if  the 
whole  load,  12  c,  were  concentrated  at  K,  a  point  chosen 
so  that  2  cl'=  10  cl.  The  same  result  is  reached  in  many 
cases  more  simply  by  figuring  the  normal  uniform  load 
as  if  concentrated  at  C,  and  then  treating  the  load  2^at 
D  as  if  it  were  on  a  separate  line,  as  in  computing  branches. 
This  is  the  best  procedure  when  grades  and  other  extra 
loads  are  superimposed  on  normal  and  regular  traffic. 


FIG.    10.  FIG.   II. 

But  the  principle  of  center  of  gravity  has  another 
and  a  broader  application. 

In  any  case  of  scattered  load  the  center  of  gravity  of 
the  system  is  the  proper  point  from  which  to  distribute 
the  power,  at  least  in  so  far  as  this  point  gives  the  mini- 
mum weight  of  copper  for  a  given  loss.  For  instance, 
in  the  line  of  Fig.  9,  E  is  the  point  from  which  the  power 
should  be  supplied,  whether  direct  from  a  generator  or 
from  a  feeder,  if  A'  B'  is  but  a  single  part  of  a  large 
system.  The  center  of  gravity  of  two  points  on  a  line  is 
found  by  the  ordinary  balancing  principle,  as  in  Fig.  9. 
The  center  of  gravity  of  any  number  of  points  in  a  plane 
is  found  by  an  extension  of  exactly  the  same  method,  as 
shown  in  Fig.  10.  I^et  there  be,  for  example,  five  load 


FUNDAMENTAL   PRINCIPLES.  T/ 

points  in  value  respectively  i,  2,  3,  4,  5;  required  the 
center  of  gravity  of  the  system. 

Take  any  two  points,  as  2  and  3,  and  find  their  mutual 
center  of  gravity,  just  as  in  Fig.  9.  This  will  be 
located  at  a  point  at  which  the  whole  value,  5,  of  the 
2-3  system  may  be  assumed  to  be  concentrated.  Now 
find  the  center  of  gravity  of  this  point  and  5;  this  will 
be  at  a  point  at  which  the  weight  will  be  10.  Then 
taking  i  and  4,  the  resultant  weight  will  be  5.  Finally, 
balance  these  resultants  and  the  center  of  gravity  of  the 
entire  system  is  found  at  15.  The  order  in  which  the 
combinations  are  made  is  of  no  consequence,  since  a  given 
system  can  have  but  one  center  of  gravity.  Now,  suppose 
the  points  i,  2,  3,  4,  5,  are  supplied  from  a  common  source 
O,  Fig.  n,  through  lines  /1? /2, /3, /4, /5.  Referring  to 
equation  (5)  the  total  weight  of  copper  in  any  line,  as  /1? 
may  be  written  W  =  K  cl* ,  wrhere  K  depends  on  the  uniform 
drop  assumed.  For  any  number  of  load  points  thus  con- 
nected to  a  center  O  2  W  =  K  2  c  /2.  But  this  is  directly 
proportional  to  the  moment  of  inertia,  2ml2,  of  the  loads 
considered  as  weights,  about  O  as  an  axis.  Now  the 
moment  of  inertia  of  any  body  about  any  axis  is  composed 
of  the  sum  of  two  terms,  viz. ,  first,  the  moment  of  inertia 
of  the  parts  of  the  body  around  its  center  of  inertia  and, 
second,  the  moment  of  inertia  of  the  whole  mass  concen- 
trated at  its  center  of  inertia,  about  the  axis  chosen. 
Therefore,  the  minimum  moment  of  inertia  for  a  given  set 
of  loads  is  obtained  when  the  axis  coincides  with  the 
center  of  inertia,  thereby  causing  the  second  term  to  dis- 
appear. Hence  the  total  weight  of  copper  required  for 
supplying,  at  a  given  loss,  any  system  of  loads  is  a  mini- 
mum when  the  system  is  fed  from  its  center  of  gravity. 
And  the  penalty  for  disregarding  this  law  is  severe,  as  will 
presently  be  shown. 

For  example,  take  the  case  of  a  circular  area  with  an 
electric  system  made  up  of  equally  and  uniformly  loaded 
lines  radiating  from  a  power  station  at  the  center.  It  has 
already  been  shown  that  the  cross  section  of  copper  needed 


iS     POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

for  a  uniformly  loaded  line  is  the  same  as  if  the  load  were 
concentrated  at  the  center.  The  weight  is  proportional  tc 
the  cross  section  multiplied  by  the  length.  In  the  circular 
distribution  of  Fig.  12,  therefore,  the  area  of  the  conduc- 
tors is  proportional  to  j-r,  the  radius  of  the  circle,  while 
their  lengths  equal  r.  Hence,  the  weight  of  copper  for 
such  a  distribution  is  directly  proportional  to  the  product 
of  these  factors  and  equals  -J  K  r2. 

If,  now,  the  system  is  fed  from  another  point  than  O  the 
center,  such  as  A,  the  weight  of  copper  will  be  propor- 
tional to  the  new  moment  of  inertia,  and,  since  this  is  made 
up  of  the  sum  of  the  terms  mentioned,  the  copper  wrill  be 

y 
doubled  when  d2=i  r2,  i.  e.  when  d=—7—  .  Itwillbemul- 

\/  2 

tipled  by  3  when  d2=r3  and  so  on,  rapidly  increasing. 
The  following  table  gives  the  relative  weights  of  copper 
corresponding  to  a  few  values,  of  W. 


=2> 


"  =3,  rV$ 

"  =4,  rVZ 

11  =5,  >Vf 

•«  =n,  rVj 

In  any  sort  of  distribution  the  mechanical  analogue 
furnishes  a  solution  of  the  copper  problem  in  the  ways 
just  indicated. 

It  at  once  appears  from  these  considerations  that  the 
cost  of  copper  runs  up  with  disastrous  rapidity  if  the  center 
of  distribution  is  distant  from  the  center  of  load.  From 
the  data  given  one  can  figure  out  readily  the  extra  invest- 
ment in  real  estate  that  it  will  pay  to  make  in  order  to  put 
the  station  near  the  center  of  load. 

The  facts  set  forth  are  a  powerful  argument  for  the 
economy  of  an  alternating  current  distribution  with  higli 
tension  feeders,  if  such  a  system  can  be  rendered  available 
for  ordinary  railway  work.  The  main  objection  to  locating 


FUNDAMENTAL   PRINCIPLES.  19 

a  center  of  supply  at  or  near  the  center  of  gravity  of  the  load 
is  the  cost  of  site.  For  a  regularly  constituted  generating 
station  this  cost  is  often  prohibitive,  so  that  it  is  far  cheaper 
to  endure  the  great  increase  of  copper  necessary  for  feed- 
ing from  a  distance.  If  the  central  plant  be  reduced  to  a 
substation  for  supplying  an  alternating  current  to  the 
working  conductors,  the  space  taken  up  is  so  trivial  that 
its  cost  is  almost  nominal..  The  reducing  transformers 
for  a  capacity  of  1000  k.  w.,  together  with  switch- 
board and  all  necessary  station  apparatus  can  easily  be 


FIG.    12. 

accommodated  in  a  room  ten  feet  square,  if  compactness  is 
necessary.  Nor  is  there  any  need  of  extreme  care  in  the 
matter  of  foundations,  since  there  is  no  moving  machinery, 
save  motors  for  ventilation,  in  such  a  substation. 

Even  if  the  day  of  alternating  motors  for  railway  service 
be  delayed  far  longer  than  now  seems  probable,  there  are 
not  a  few  cases  in  which  substations  with  motor-generators 
are  preferable  in  point  of  economy  to  an  immense  invest- 
ment in  feeders.  At  present  prices  of  apparatus  such  a 
condition  will  be  met  far  oftener  than  would  at  first  glance 
seem  probable.  In  large  cities,  where  there  is  a  vstrong 
and  growing  tendency  to  force  all  feed  wires  underground, 


20     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

the  cost  of  installing  and  keeping  up  conduits  adds  very 
materially  to  the  disadvantage  of  elaborate  feeding  systems 
from  a  distant  point.  • 

Another  class  of  cases  in  which  special  attention  to  the 
location  of  power  station  is  needed  may  be  found  in  the 
interurban  and  cross  country  roads  now  becoming  common. 

Generally  the  distribution  is  linear  or  branched,  rather 
than  a  network.  We  should  not,  however,  assume  that 
the  power  station  should  lie  at  the  middle,  end  or  any 
other  point  on  the  line  of  the  road.  It  very  often  happens 
that  the  center  of  gravity  of  the  load,  which  is  the  most 
economical  point  for  distribution,  as  we  have  just  seen,  is 
not  on  the  line  at  all.  For  example,  take  the  line  shown 
in  Fig.  13.  It  consists  of  three  sections  connecting,  we 


FIG.  13. 

may  suppose,  four  towns,  A,  B,  C,  D.  The  configuration  of 
the  system  is  here  determined  by  the  topography  of  the 
region,  the  amount  of  business  at  each  point,  and  similar 
considerations  familiar  in  the  art  of  railway  location.  We 
may  suppose  the  load  of  each  section  concentrated  at  its 
middle  point  as  before,  forming  the  load  points,  a,  b,  c. 
Suppose  the  loads  to  be  as  follows  :  a  =  15,  b  =  10,  c  =  5. 
These  loads  may  be  taken  in  any  convenient  units  pro- 
vided the  same  units  are  used  throughout. 

Now,  proceeding  as  before,  draw  b  c  and  locate  the 
center  of  gravity  of  the  loads,  b  and  c.  This  proves  to  be 
d,  where  the  concentrated  load  is  15.  Then  drawing  a  d, 
the  center  of  gravity  of  the  system  is  found  to  be  at  O,  quite 
off  the  line  of  the  road,  although  not  inconveniently  distant 
from  B.  In  other  instances  the  center  of  gravity  might 
very  readily  be  as  far  from  any  of  the  towns,  A,  B,  C,  D,. 


FUNDAMENTAL    PRINCIPLES.  21 

as  each  is  from  its  neighbor.  This  example,  however, 
shows  a  common  characteristic  of  long  lines. 

The  network  type  of  distribution  found  in  railway  prac- 
tice is  quite  different  in  character  and  needs  from  a  light- 
ing network.  It  is,  save  in  a  few  instances,  such  as  Fig, 
4  (see  page  4) ,  much  less  complex  and  is  always  much  more 
irregular  in  load.  In  a  well  ordered  central  station  for 
electric  lighting,  every  street  in  the  business  district  has 
its  main,  and  the  load,  while  far  from  regular,  does  not 
exhibit  the  extreme  variations  found  in  electric  railway 
work. 

The  general  solution  of  even'  a  simple  network,  to  find 
the  current  (and  thence  the  drop)  in  each  line  due  to  one 
or  more  known  load  points,  involves  a  most  forbidding 
amount  of  tedious  computation.  But  for  the  purpose  in 
hand  exact  solutions  are  not  needed  so  much  as  easy  ap- 
proximations. 

Consider,  for  example, the  simple  network  of  conductors 
shown  in  Fig.  14.  A  is  here  the  source  of  supply,  either 
the  station  or  the  end  of  a  feeder.  The  load  is  distributed 
along  the  lines,  A  D,  A  K,  D  E,  D  F,  K  F,  D  C,  F  B  and 
C  B.  Such  a  circuit  may  be  said  to  consist  of  three  meshes, 
and  it  contains  eight  currents  which  we  may  call  i^ ,  t2  etc. 
In  lighting  practice  it  is  necessary,  knowing  the  load  to  be 
supplied  by  each  line,  to  figure  the  conductors  so  as  to 
maintain  uniform  voltage  throughout  the  network.  This 
involves  algebraic  processes  too  complex  for  convenient  use; 
in  fact  the  complete  solution  is  a  very  pretty  problem  in 
determinants,  which  those  interested  may  find  elucidated  in 
Maxwell's  "Treatise  on  Klectricity  and  Magnetism,"  and 
somewhat  simplified  in  a  paper  by  Herzog  and  Stark,  pub- 
lished in  1890.  For  railway  work  the  conditions  are, 
fortunately,  simpler.  We  know,  or  can  assume  with  suffi- 
cient accuracy,  the  normal  distributed  load  on  each  of  the 
lines.  But  we  are  absolved  from  any  necessity  for  keeping 
closely  uniform  voltage  throughout  the  system,  since,  even 
were  it  a  matter  of  more  importance  than  it  ever  is,  it 
could  only  be  accomplished  by  using  an  enormous  excess  of 


22     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

copper,  for  a  large  part  of  the  load  is  liable  at  any  time  to 
be  concentrated  on  almost  any  part  of  the  network. 

Two  conditions  must  at  all  events  be  fulfilled.  First, 
each  one  of  the  lines,  A  D,  A  K,  etc.,  must  be  able  to 
carry  its  own  proper  load  without  exceeding  a  standard 
drop;  and,  second,  the  sum  of  the  distributed  loads  must  be 
carried  at  certain  points,  which  can  be  approximately  pre- 
judged, without  exceeding  a  certain  maximum  drop. 

It  must  be  noted  that  the  conducting  system  of  a  rail- 
way differs  from  that  of  a  lighting  plant  in  having  a  much 
greater  proportion  of  feeders  to  mains.  In  fact  the  working 


FIG.  14. 

conductor  of  a  railway  is  generally  of  quite  limited  carrying 
capacity.  Practically,  in  laying  out  a  network  like  that  of 
Fig.  14,  one  has  to  cut  loose  from  lighting  precedents  and 
deal  with  a  special  problem. 

Following  the  first  of  the  conditions  just  named,  a 
convenient  first  step  is  to  compute  the  conductors  as  iso- 
lated lines,  on  the  assumption  that  tlt  z*2,  z3,  etc.,  are  the 
currents  due  to  the  normal  load  on  each  line.  This  fur- 
nishes the  skeleton,  as  it  were,  of  the  conducting  system. 
This  work  can  often  be  simplified  by  bearing  in  mind  the 
main  lines  of  traffic  and  treating  as  one  their  component 
conductors.  For  instance,  in  Fig.  14,  if  A  be  the  station 


FUNDAMENTAL    PRINCIPLE?  23 

it  may  be  convenient  to  take  A  D  C  B  as  a  single  conductor 
carrying  a  load  z1  +  z  6  -f  i 8 ,  and  A  E  F  B  as  another  loaded 
with  2*2+  z*4 +  z  7.  DEandDFmay  then  be  taken  sepa- 
rately. 

Now,  this  skeleton  must  be  padded  with  reference  to 
the  second  condition  mentioned.  Suppose  that  traffic  is 
liable  to  be  congested  at  or  near  B.  This  point  is  fed  by 
the  two  main  lines  in  multiple.  If  the  drop  chosen  for 
these  in  making  the  skeleton  would  mean  a  drop  at  B 
sufficient  to  seriously  impede  traffic,  enough  copper  must 
be  added  to  relieve  this  condition.  Just  where  this  addi- 
tion should  be  made  requires  the  exercise  of  considerable 
discretion.  If  F  is  a  point  where  congestion  is  also  to  be 
feared  the  line,  A  D  F,  should  be  strengthened,  being  the 
nearest  route.  If  C  be  threatened,  ADC  should  be  rein- 
forced. In  either  case  the  addition  should  be  sufficient  to 
put  B  out  of  danger.  In  any  case  z  3  and  z  5  should  be  con- 
sidered with  reference  to  the  lines,  A  D  and  A  K,  and  the 
drops  in  D  K  and  D  F  so  taken  as  to  keep  them  at  good 
working  pressure  in  spite  of  any  excessive  demands  near 
the  terminus  of  the  system.  In  other  words,  for  railway 
work  it  is  nearly  always  possible  to  split  up  a  network 
into  a  combination  of  linear  systems  and  branches,  since 
the  loads  are,  or  may  be,  so  uncertain  that  fine  discrimina- 
tion in  minor  lines  is  out  of  the  question. 

A  good  development  of  this  splitting  principle  may  be 
found  in  Fig.  15,  which  is  a  network  of  three  meshes  com- 
posed of  two  parallel  lines,  A  and  B,  cross  tied  by  the  lines, 
C  D,  E  F,  G  H,  I  J.  Let  A  be  a  feeder  and  B  the  trolley 
wire  and  we  have  the  well  known  "ladder"  system  of 
feeding  in.  As,  in  practice,  CD,  E  F,  etc. ,  are  very  short 
compared  with  C  E,  E  G,  etc. ,  the  system  may  be  regarded 
as  composed  of  A  and  B  in  parallel,  the  only  qualification 
being  due  consideration  of  the  possible  drop  in  B  between 
a  load  point  and  the  two  nearest  feeding  points.  But  we 
may  suppose  A  and  B  to  run  in  adjacent  streets  and  the 
former  to  be  connected*  to  another  trolley  wire  on  its  own 
street,  then  a  track  to  run  along  GH,  and  so  on  until 


24     POWER    DISTRIBUTION   FOR   ELECTRIC    RAILROADS. 

the  full  network  is  developed.  At  each  stage  of  compli- 
cation the  system  may  be  considered  as  composed  of  one 
or  more  mains  with  branches,  without  sensible  error,  the 
inaccuracy  of  the  assumption  being  negligible  compared 
with  the  uncertainty  produced  by  the  irregular  load. 

The  variations  of  load  in  an  electric  railway  system 
are  so  prodigious  as  to  render  the  most  careful  calculations 
only  roughly  approximate.  They  are,  in  general,  of  three 
kinds.  First,  the  momentary  variations  due  to  accidental 
changes  of  load  incident  to  the  nature  of  the  service. 
Second,  periodic  general  variation  of  the  aggregate  load 
caused  by  the  varying  conditions  of  service  throughout  the 
day.  Third,  shifting  of  the  load  to  various  points  of  the 


FIG.    15. 

system,  concurrent  with  the  daily  variations  in  total  load, 
but  bearing  to  them  no  simple  relation. 

The  momentary  variations  are  constantly  occurring 
from  minute  to  minute,  almost  from  second  to  second. 
They  are  most  considerable  in  street  railway  systems  oper- 
ating but  few  cars,  and  their  amplitude  may  then  be  equal 
even  to  the  maximum  total  load,  and  occur  in  a  fraction  of 
a  minute.  Such  a  condition  may  easily  exist  in  a  plant 
operating  eight  or  ten  cars.  As  the  number  of  cars  in- 
creases, the  chance  of  so  great  variations  diminishes, 
although  somewhat  slowly.  In  very  large  systems,  the  ex- 
treme amplitude  of  these  oscillations  of  load  may  be  re- 
duced to  twenty  or  twenty-five  per  cent,  of  the  total  load, 
but  they  can  never  disappear  entirely.  Their  effect  on  the 
design  of  the  conducting  system  is  but  small,  for  the  volt- 
age does  not  have  to  be  kept  closely  uniform,  and  the  con- 


FUNDAMENTAL   PRINCIPLES.  25 

ductors  will  be  laid  out  for  the  average  load  based  on  the 
average  consumption  of  energy  per  car.  With  a  normal 
drop  so  computed  and  with  care  taken  to  allow  a  reason- 
able margin  for  maximum  loads,  these  variations  of  the 
first  class  need  not  constitute  a  serious  embarrassment. 

The  diurnal  changes  of  load  based  on  average  readings 
in  which  the  minor  oscillations  are  suppressed,  are  great  in 
amount  and  of  much  interest.  They  are  due  to  the  habits 
and  occupations  of  the  community  served,  and  often  exhibit 
very  curious  peculiarities.  Further,  they  are  almost  as 
strongly  marked  in  very  large  systems  as  in  quite  small 
ones  and  serve  to  determine  the  relation  of  average  to  max- 
imum load,  which  in  turn  determines  the  allowance  which 
must  be  made  for  drop  at  extreme  loads.  Even  under  very 
favorable  circumstances  the  difference  between  average  and 
maximum  load  is  great.  This  is  very  forcibly  shown  in 
Fig.  1 6,  which  gives  the  load  line  on  one  of  the  largest 
electric  railway  systems  for  a  December  day,  just  before 
the  holidays. 

The  minimum  load  is  quite  uniform  from  2  A.  M.  until 
5  A.  M.  and  is  only  about  six  per  cent  of  the  maximum.  At 
about  5  A.  M.  the  load  comes  on  quite  suddenly  and  con- 
tinues to  rise  until  about  9  A.  M. ,  when  it  begins  to  fall, 
and  keeps  diminishing  until  about  2  p.  M.  Then  it  rises, 
slowly  at  first  and  then  more  rapidly  until  it  reaches  a 
second  maximum,  about  equal  to  the  first,  at  6  p.  M.  Then 
it  falls  somewhat  irregularly  until  only  the  night  cars  are 
left. 

The  average  load  for  the  twenty-four  hours  is  about 
six-tenths  of  that  at  the  two  maxima.  This  difference  is 
what  must  be  kept  in  mind  in  providing  a  due  factor  of 
safety  in  the  conductors.  The  load  line  is  not,  of  course, 
invariable,  being  subject  both  to  accidental  and  yearly  varia- 
tions, but,  in  spite  of  these,  it  preserves  its  characteristics 
and  the  value  of  its'*  load  factor"  with  remarkable  uni- 
formity. In  small  systems  there  are  practically  no  night 
cars,  the  service  being  generally  about  eighteen  hours. 
Were  such  the  case  in  Fig.  16,  the  "load  factor  "  would  be 


26     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

materially  improved,  rising  in  fact  to  about  three-fourths 
on  this  supposition.  But  in  small  plants  the  day  mimi- 
mum  is  relatively  smaller  than  in  Fig.  16,  so  that  the  load 
factor  is  worse.  Indeed  it  only  too  frequently  falls  to  one- 
quarter  or  one-third  in  roads  operating  five  to  ten  cars. 
Any  value  of  load  factor  over  one-half  may  be  considered 
good  in  any  but  the  largest  plants. 

In  long  roads  operating  a  few  large  cars  or  trains  at 


20,000 


6  12 

P.M.  Mid. 

Street  Railway  Journal 


FIG.  16. 


high  speed,  the  load  is  subject  to  smaller  casual  variations,, 
but  the  load  factor  is  apt  to  be  low  by  reason  of  the  great 
change  made  by  the  stopping  or  starting  of  a  single  load  unit. 
The  load  during  the  period  of  acceleration  is  likely  to  be 
about  double  the  running  load  even  with  carefully  handled 
motors,  and  as  this  period  is  often  several  minutes,  there  is 
an  excellent  chance  for  the  superposition  of  several  such 
loads. 

More  serious  than  any  others  are  the  variations  in  the 
location  of  load,  since  these  may  cause  a  heavy  call  for 


FUNDAMENTAL   PRINCIPLES.  27 

power  at  some  distant  part  of  the  system.  Such  shifting 
of  the  load  occurs  in  nearly  all  cases  of  linear  distribution, 
and  has  already  been  noted,  but  it  also  occurs  on  all  sorts 
of  systems,  and  is  the  more  serious  as  it  is  less  to  be  regu- 
larly expected.  A  single  blockade  may  fill  a  limited  dis- 
trict with  stalled  cars,  and  when  at  last  it  is  broken  the  call 
for  power  is  of  a  most  abnormal  kind.  It  does  not  appear 
strongly  marked  on  the  load  line,  but  shows  in  the  shifting 
of  load  from  one  feeder  to  another.  On  systems  of  moderate 
size  this  shifting  of  load  may  be  very  serious.  For  example, 
through  the  baseball  season  many  roads  will  find  nearly 
their  full  output  demanded  at  the  ball  park  once  or  twice 
a  week.  The  next  maximum  output  may  be  at  the  other 
end  of  the  system,  to  accommodate  some  special  celebration. 
Even  in  a  large  network,  at  certain  hours,  during,  and  just 
before,  maximum  load,  the  bulk  of  the  load  will  be  within 
a  small  district,  and  within  the  same  district  only  when  the 
same  causes  produce  the  shifting. 

This  wandering  of  the  main  load  over  the  system 
is  one  of  the  most  exasperating  factors  in  the  design  of  the 
conductors.  It  may  easily  amount  to  the  concentration  of  a 
quarter  or  third  of  the  total  load  at  some  quite  unexpected 
point.  It  can  be  dealt  with  only  by  a  minute  study  of  the 
local  conditions,  which  generally  will  furnish  some  clue  to 
the  probable  magnitude  and  position  of  such  wandering 
loads.  Whatever  may  be  the  general  conditions  of  drop, 
the  conductors  must  be  so  distributed  as  to  prevent  the  sys- 
tem breaking  down  when  loaded  in  some  abnormal  man- 
ner at  some  unusual  point.  No  theory  can  take  account 
of  such  occurrences;  their  ill  effects  can  be  obviated  only 
by  good  judgment,  which  is  of  more  value  than  many 
theories. 


CHAPTER  II. 

THE   RETURN   CIRCUIT. 

The  outgoing  circuit  of  an  electric  railway  has  just 
been  discussed  in  its  more  general  relations.  Before  invest- 
igating the  proportioning  of  the  working  conductors  it  is 
necessary  to  look  into  the  return  circuit.  Up  to  this  point 
it  has  been  assumed  that  this  is  similar  to  the  outgoing 
system  as  it  is  in  the  case  of  motor  systems  in  general. 

In  nearly  all  electric  railway  practice  it  has  been  the 
custom  to  employ  the  rails  and  earth  as  the  return  circuit, 
since  the  former  are  good  conductors  and  necessarily  in 
contact  with  the  car  wheels,  and  the  latter  is  as  necessarily 
in  contact  with  the  rails. 

In  some  cases  two  running  contacts  are  employed  as 
in  the  double  trolley  system,  conduit  roads,  some  recent 
elevated  roads,  and  the  like,  but  in  most  instances  the 
total  circuit  of  any  railroad  consists  of  the  outgoing  system 
of  copper  conductors  and  a  return  circuit  consisting  of  the 
rails  and  their  environment. 

Now  the  conductivity  of  an  iron  or  steel  rail  is  com- 
puted with  tolerable  ease,  but  the  rest  of  this  heterogeneous 
system  is  most  uncertain.  It  consists,  near  the  surface,  of 
bond  copper,  tarnished  surfaces,  iron  rust,  rock,  dirt,  dirty 
water,  mud,  wet  wood  and  promiscuous  filth,  and  deeper 
down  of  all  sorts  of  earthy  material,  and  in  cities  various 
sorts  of  pipes  for  gas,  water,  etc. 

In  the  early  days  of  electric  railroading  the  resistance 
of  this  strange  assortment  was  assumed  to  be  zero  on  the 
theory  that  the  earth  was  the  conductor  concerned  and  was 
practically  of  infinite  cross  section.  This  was  shockingly 
far  from  the  truth  and  although  data  are  rather  scarce,  we 


THE   RETURN   CIRCUIT.  29 

may  properly  take  up  the  return  circuit  piecemeal  and  see 
what  the  actual  state  of  things  may  be. 

First  as  to  the  rails.  Mild  rail  steel  is  a  very  fair 
conductor.  Weight  for  weight  it  is,  comparing  the  com- 
mercial metals,  just  about  one-seventh  as  good  a  conductor 
as  copper.  Now  a  copper  wire  weighing  one  pound  per 
yard  has  an  area  of  about  110,000  c.  m.;  hence -an  iron 
bar  weighing  one  pound  per  yard  is  equivalent  to  about 
16,000  c.  m.  of  copper,  very  nearly  equal  to  No.  8  B 
&  S  gauge.  This  enables  us  at  once  to  get  the  equivalent 
conductivity  of  any  rail  neglecting  the  joints. 

The  resistance  of  a  copper  wire  of  16.000  c.  m.  is 
roughly  six-tenths  of  an  ohm  per  thousand  feet.  Hence  the 
resistance  of  any  single  rail  in  ohms  is,  per  thousand  feet 

R  =  —         where  W  is  the  weight  per  yard. 

Or  since  two  rails  form  the  track  R  =  ~- 

That  is,  if  the  rail  used  weighs  sixty  pounds  per  yard  the 
track  resistance  is  approximately  -$$-$  ohm  per  thousand  feet. 
For  convenience  the  relation  between  weight  of  rail  and 
equivalent  copper  is  plotted  in  Fig.  17.  The  maximum 
figure  is  for  mild  rail  steel.  Of  late  there  has  been  a  tend- 
ency to  use  a  harder  steel  rather  high  in  manganese.  This 
lowers  the  conductivity  by  no  small  amount,  sometimes  to 
one-tenth  that  of  copper,  for  which  the  minimum  in  Fig. 
17  is  arranged.  In  close  figuring  the-  conductivity  should 
be  measured,  and  specified  in  ordering  rails. 

These  relations  enable  one  to  figure  the  drop  in  the 
track,  neglecting  joints i  by  the  formulae  already  given. 
For  this  purpose  the  distance  in  the  formula  should  be,  of 
course,  the  actual  length  of  track,  not  the  double  length  as 
when  a  return  circuit  of  copper  is  figured.  Thus  one 
would  separate  the  outgoing  and  return  circuits  and  com- 
pute the  drop  in  them  separately.  For  simplicity  it  is 
however  desirable  to  make  allowance  if  possible  for  the 
return  circuit,  incorporating  it  in  the  constant  of  the 
original  formula  so  as  to  make  but  a  single  calculation. 


30    POWKR   DISTRIBUTION   FOR   EI^CTRIC   RAILROADS. 

The  figures  just  given  emphasize  with  tremendous  force 
the  need  of  thorough  bonding  of  the  track  in  order  to  take 
advantage  of  its  immense  conductivity.  In  the  early  elec- 
tric railways  this  was  terribly  neglected,  the  bond  wires 
sometimes  being  as  small  as  No.  6  and  even  of  galvanized 
iron.  Bonding  is  of  very  various  character.  Its  most 
rudimentary  form  is  shown  in  Fig.  18.  In  this  case  the 


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MG.  17. 

bouds  merely  united  the  ends  of  adjacent  rails,  each  line  of 
rails  being  bonded  separately.  The  improvement  of  Fig, 
19  is  quite  obvious,  for  in  Fig.  18  a  single  break  compelled 
one  rail  to  carry  the  return  load.  The  cross  bonding  of 
Fig.  19  adds  somewhat  to  the  weight  of  copper  required,' 
but  ties  the  rails  together  so  that  no  single  break  can  be 
serious  and  nothing  save  a  break  from  both  rails  on  the 
same  side  of  the  same  joint  can  really  interrupt  the  circuit. 
A  very  large  amount  of  track  has  been  so  bonded,  al- 
though at  present  the  usual  construction  is  shown  in  Fig. 


THE   RETURN  CIRCUIT.  $1 

20.  The  supplementary  wire  effectively  prevents  ' '  dead 
rails.*'  In  modern  practice  the  bond  wires  are  often  as 
heavy  as  No.  oooo,  and  are  generally  tinned  to  prevent 
corrosion.  All  joints  in  the  wire  are  soldered  and  the  rail 
contacts  made  as  perfect  as  possible.  It  is  perfectly  clear 
that  the  supplementary  wire  is  of  little  value  as  a  con- 


FIG.  18. 


FIG.  19. 


FIG.   20. 


FIG.    21. 

ductor  compared  with  the  rails,  but  it  is  of  service  in  miti- 
gating the  effects  of  bad  joints.  In  a  few  cases  this  supple- 
mentary wire  is  reinforced  by  a  heavy  copper  conductor  laid 
alongside  the  track  and  connected  at  intervals  to  the  sup- 
plementary wire  as  shown  in  Fig.  21.  If  the  joints  made 
by  the  bonds  and  rail  are  very  bad  this  extra  copper  may 
be  of  service,  but  good  joints  render  it  quite  unnecessary. 
The  value  of  the  rails  as  conductors  is  so  great  that  every 
effort  should  be  made  to  utilize  them  to  the  fullest  possible 
extent. 


32     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

The  seriousness  of  the  joint  question  may  be  seen  by 
a  moment's  reflection  upon  the  data  already  given.  There 
are  about  thirty -three  joints  per  thousand  feet  of  rail.  This 
means  sixty-six  contacts  per  thousand  feet  between  rail  and 
bond,  in  addition  to  the  resistance  of  the  bond  wire  itself. 
Now,  the  resistance  of  a  sixty  pound  rail  per  thousand  feet 
is,  as  we  have  seen,  only  y^  ohm,  in  decimals  o.oi.  If 
there  should  be  even  one-ten-thousandth  of  an  ohm  resist- 
ance in  each  joint  between  bond  and  rail,  the  total  resistance 
would  rise  to  0.016  ohm  per  thousand  feet.  Add  to  this,  the 
actual  resistance  of,  say,  sixty  feet  of  bonding  wire  No.  o, 
and  the  total  foots  up  to  0.022  ohm,  more  than  doubling 
the  original  resistance.  If  the  joints  were  here  and  there 
quite  imperfect,  as  generally  happens,  the  rail  resistance 
might  easily  be  increased  far  more. 

One  would  be  thought  lacking  in  common  sense  who 
needlessly  doubled  the  resistance  of  an  overhead  circuit, 
but  in  the  rail  circuit  far  more  atrocious  blunders  are  only 
too  common.  A  few  years  ago  it  was  frequent  enough  to 
find  bond  wire  simply  driven  through  a  hole  in  the  web  of 
the  rail  and  headed  on  the  outside.  Fortunately,  the  need 
of  care  here  is  now  better  realized  and  in  the  last  few  years 
the  name  of  the  rail  bond  is  legion.  Most  of  the  contacts 
are  modified  rivets,  not  infrequently  supplied  with  some 
sort  of  wedging  device  to  ensure  a  tight  contact.  They 
are,  most  of  them,  good  enough  if  properly  applied,  but  a 
careless  workman  can  easily  destroy  the  usefulness  of  even 
the  best  bonds.  The  bond  contact  proper  is  often  quite 
distinct  from  the  bond  wire  and  is  generally  given  a  greater 
cross  section  than  the  latter,  to  ensure  an  ample  contact 
with  the  rail.  Figs.  22  to  25,  inclusive,  show  some  of  the 
best  current  forms  of  bonds.  Fig.  25,  the  "plastic" 
bond,  is  composed  cf  a  layer  of  a  species  of  amalgam  re- 
tained by  an  outer  wall  of  cork  and  squeezed  into  intimate 
contact  with  rail  and  channel  plate.  It  gives  a  singularly 
low  resistance  contact. 

As  to  the  real  resistance  of  a  bonding  contact,  experi- 
ments, as  might  be  expected,  vary  enormously.     The  re- 


RETURN   CIRCUIT. 


33 


sistance  of  the  bonding  wire  is,  of  course,  determinate,  but 
that  of  the  contact  is  most  irregular,  varying  with  every 


FIG.    22. — COLUMBIA   BOND. 


o     o 


Q      1 


FIG.  23. — CROWN  STRANDED  BOND. 


FIG.  23A. — CROWN  BOND. 


FIG.    24. — BROWN  PLASTIC  BOND. 


FIG.    25. — BRYAN  BOND 


kind  and  size  of  bond  and  with  the  thoroughness  with 
which  the  mechanical  work  is  done.  No  part  of  electric 
railway  construction  deserves  more  careful  attention.  Cull- 


34      POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

ing  the  values  of  bond  resistances  from  experiments  on  the 
bonds  shown  we  get  the  following  table  : 

BOND  RESISTANCES. 

Fig.  22    =  0.000131  ohm. 
"     23    =  o.oooi 

"       23  A  =  O.OOO247 
"       24     =  0.00006 
"       25      —0.000175 

These  resistances  are  for  the  complete  bonds  newly  set. 

As  nearly  as  may  be  judged,  the  resistance  of  a  single 
contact,  carefully  made,  can  be  counted  on  to  be  consider- 
ably less  than  .001  ohm.  With  bond  plugs  of  large  surface 
well  set,  it  would  seem  safe  to  count  upon  a  resistance  not 
exceeding  .0002  ohm.  per  contact. 

The  bonding  wires  should  be  as  short  as  can  be  con- 
veniently handled.  The  advantage  of  lessened  length 
appears  strongly  in  the  results  from  Fig.  23.  Such  bonds 
under  the  fish  plates  are  more  dificult  to  apply  than  bonds 
around  the  fish  plates,  but  are  of  low  resistance  and  well 
protected.  As  to  size,  there  is  little  reason  for  using  any- 
thing smaller  than  No.  ooo  or  No.  oooo.  With  about 
a  foot  of  No.  oooo  at  each  joint,  and  thorough  contacts 
carefully  made,  the  resistance  of  bonds  ought  to  be  about 
as  follows  per  thousand  feet. 

66  bond  contacts  =  .0132 
33  ft.  oooo  wire  =  .00165 


Total  0.0148  ohm. 

This  is  about  one  and  a  half  times  the  resistance  of  a  thou- 
sand feet  of  sixty  pound  rail  and  corresponds  well  with 
actual  tests  of  well  bonded  track.  It  is  quite  near  the  truth 
to  assume  that  under  average  circumstances  of  good  con- 
struction the  bond  wire  and  contact  resistance  may  aggregate 
about  twice  the  resistance  of  the  rails  themselves. 

As  regards  the  earth  there  is  great  misconception  both 
as  to  its  conducting  power  and  the  part  it  takes  in  modify- 
ing the  rail  and  bond  resistance  which  we  have  just  been 
considering.  Outside  of  the  metals  there  are  no  sub- 
stances that  have  even  fair  conducting  properties.  That 


THE   RETURN  CIRCUIT.  35 

is,  all  other  so-called  conductors  are  very  bad  compared  even 
with  a  relatively  poor  conductor  like  iron.  For  example, 
carbon  in  the  form  of  graphite  or  gas  coke,  is  usually  consid- 
ered a  very  fair  conductor,  yet  it  has  several  hundred  times 
the  resistance  of  iron,  while  nitric  acid  and  dilute  sulphuric- 
acid,  the  best  conductors  among  electrolytes,  have  many 
thousand  times  the  resistance  of  iron.  The  acid  last  men- 
tioned has  a  specific  resistance  of  about  0.4  ohm  for  a 
cubic  centimeter,  while  the  resistance  of  a  cubic  centimeter 
of  iron  is  only  o.ooooi  ohm.  Water,  even  when  dirty  as  it 
is  found  in  the  streets,  would  show  a  specific  resistance  of 
1000  ohms  or  more.  Earth,  rock  and  other  miscellaneous 
components  of  the  ground  are  even  worse,  so  that  it  is  at 
once  fairly  evident  that  it  would  take  an  enormous  con- 
ducting mass  even  of  water  to  approximate  the  conductiv- 
ity of  a  line  of  rails. 

Even  in  theory  the  mass  of  earth  really  available  for 
conducting  purposes  is  somewhat  limited,  for  if  a  current 
be  passed  between  two  earth  plates,  the  current  density  de- 
creases very  rapidly  as  the  lines  of  flow  depart  from  the 
direct  path  between  the  plates.  It  has  long  ago  been 
shown,  too,  that  when  such  a  current  is  established  be- 
tween, let  us  say,  a  pair  of  metallic  balls  sunk  in  the  earth, 
the  resistance  of  the  circuit  does  not  vary  much  with  the 
distance  apart  of  the  terminals,  but  depends  greatly  on  the 
surface  of  the  ground  connections.  Numerous  experiments, 
too,  have  shown  that  the  earth  is  so  heterogeneous,  so 
broken  up  into  strata  of  varying  conductivity,  that  the 
current  flow  takes  place  mainly  along  special  lines,  the 
general  mass  taking  very  little  part  in  the  action.  If,  for 
example,  a  ledge  of  rock  is  in  the  line  between  earth  plates, 
save  for  possible  crevices  filled  with  water,  it  is  practically 
a  non-conductor. 

At  various  times  and  places  the  value  of  a  true  earth 
return  for  railway  and  similar  work  has  been  thoroughly 
tried  and  has  generally  been  found  to  be  practically  nil. 
In  two  cases  the  ground  plates  were  sunk  in  considerable 
rivers  which  formed  return  circuits  for  lines  in  each  case 


36     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

about  four  miles  in  length.  The  ground  plates  themselves 
were  of  ample  area,  in  one  experiment  several  hundred 
square  feet,  and  gave  every  opportunity  for  good  contact 
with  the  water.  The  applied  voltage  in  each  set  of  ex- 
periments was  500  to  550.  The  resulting  currents  were 
insignificant  and  the  resistance  of  the  earth  return  proved 
in  one  case  to  be  about  85  ohms,  in  the  other  but  a  few 
ohms  less. 

In  another  more  recent  experiment  the  terminal  sta- 
tions were  about  3000  ft.  apart.  An  attempt  had  been  made 
to  use  an  earth  return  for  a  motor  circuit,  with  the  usual 
result,  and  the  failure  led  to  investigation.  The  experi- 
ment was  arranged  as  in  Fig.  26.  At  A  and  B  were  care- 
fully arranged  ground  plates  in  duplicate.  One  of  each 
pair  was  sunk  in  a  well,  the  other  imbedded  in  a  mass  of 
iron  filings  in  damp  earth.  At  i,  2,  3,  4,  5,  stations  500 
ft.  apart,  grounds  were  made  by  driving  large  iron  bars 
deep  into  the  earth.  The  voltages  employed  were  vari- 
ous, from  60  to  150  volts  direct  current,  and  alternating 
current  from  a  small  induction  coil.  The  results  were 
nearly  coincident  in  all  the  sets  of  experiments  and  showed 
the  following  curious  state  of  affairs: 

Stations.  "Res.  ohms. 

A  .  .  B  92.4        Ground  plates  alone. 

A.  .B  121.  o        Well  plates  alone. 

A  .  .  B  66. 8        Both  well  and  ground  plates. 

A  .  .  I  201.6 

«          A  .  .  2  374.0 

A  .  .  3  92. 

A  .  .  4  506.3 

A  .  .  5  180.0 

The  resistance  is  evidently  not  a  function  of  the  distance 
nor  of  anything  else  that  is  at  all  obvious.  The  only 
feature  that  is  what  might  be  expected,  is  the  tolerably 
regular  effect  of  putting  both  sets  of  earth  plates  in  parallel 
as  exhibited  in  the  first  three  lines  of  the  table.  The  re- 
sistances at  the  intermediate  stations  show  how  hopeless 
it  is  to  predicate  anything  of  earth  resistance  except  that 


THE   RETURN   CIRCUIT.  37 

it  is  too  high  to  be  of  any  practical  use  save  for  trivial 
currents  such  as  are  employed  in  telegraphy. 

Imagine  the  stations  A  and  B,  Fig.  26,  to  be  con- 
nected by  a  track  consisting  of  a  pair  of  sixty  pound  rails 
thoroughly  connected  and  put  in  parallel  with  the  circuit 
via  the  earth  connections.  At  best  this  has  a  resistance 
of  66.8  ohms  while  that  of  the  track  should,  be  at  worst 
only  a  few  tenths  of  an  ohm.  Following  the  ordinary  law 
of  derived  circuits,  it  is  clear  that  the  current  returning  via 

A~_! *. 1 i 1 B 

TflG.   26. 

the  earth  is  only  a  minute  fraction  of  one  per  cent  of  the 
whole.  If  the  track  could  be  continuously  in  good  con- 
tact with  the  earth  throughout  its  length  somewhat  more 
current  might  be  coaxed  into  the  earth  return  by  taking  ad- 
vantage of  all  the  fairly  conducting  streaks  and  strata.  In 
rare  instances  the  earth  under  the  track  has  been  found  in 
such  condition  as  to  have  a  material  amount  of  conductiv- 
ity, enough  to  lessen  the  drop  through  the  rails  very  per- 
ceptibly. Such  cases,  while  well  authenticated,  are  so 
uncommon  as  to  be  of  small  value  save  in  showing  the 
enormous  irregularity  of  earth  resistance,  and  the  utter 
lack  of  any  well  defined  laws  governing  it.  And  in  prac- 
tice, track  is  so  laid  that  it  is  not  in  good  electrical  con- 
tact with  the  earth  as  a  whole.  Fig.  27  shows  in  section 
a  type  of  track  construction  which  has  been  very  widely 
used.  The  rail  is  laid  upon  a  longitudinal  stringer  tim- 
ber to  which  it  is  spiked  firmly.  The  stringer  is  secured 
to  the  cross  ties  by  angle  irons.  The  ties  are  well  tamped 
with  clean  sharp  gravel  which  is  packed  around  them  and 
the  stringer,  and  forms  a  foundation  for  paving  of  block 
granite  set  closely  in  upon  the  rail.  Here  the  material  in 
contact  with  the  rail  and  surrounding  it  for  some  space 
is  very  badly  conducting  except  when  the  track  is 
flooded. 

Fig.  28  shows  another  track  construction,  which  would 
appear  to  give  even  worse  conduction  between  rail  and 


38     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

earth  than  Fig.  27.  The  rails  are  here  supported  at  each 
tie  by  cast  iron  chairs,  without  an  intermediate  stringer, 
and  the  ties  are  set  in  concrete,  while  rail  and  chair  are 
surrounded  by  coarse  gravel  on  which  the  paving  is  laid. 
In  no  modern  track  is  the  rail  in  contact  with  better  con- 
ductors than  hard  wood,  gravel  or  stone.  Consequently 
there  is  very  little  tendency  for  current  to  be  shunted  from 
rails  to  earth,  unless  the  former  are  very  badly  bonded, 


FIG.  27. 

for  the  paths  in  derivation  are  bad  and  there  is  little  differ- 
ence of  potential  between  any  two  points  of  the  track  to 
impel  branch  currents  of  any  kind.  Of  course,  if  one  at- 
tempts to  use  the  two  rails  as  outgoing  and  return  leads, 
the  condition  is  wholly  changed,  for  the  full  difference 
of  potential  then  exists  between  two  neighboring  rails 
and  there  must  be  a  very  large  amount  of  leakage.  In 
fact,  if  there  is  any  considerable  difference  of  potential  be- 
tween the  rails  or  between  them  and  any  other  conductor, 
there  will  be  a  perceptible  flow  of  current,  even  through 
as  bad  a  conductor  as  "damp  gravel,  if  the  path  be  not 
too  long. 


THE   RETURN   CIRCUIT. 


39 


Thus  it  is  that  while  ground  plates  along  the  track 
according  to  early  usage  are  insignificant  in  modifying  the 
conductivity  of  the  return  circuit,  there  may  be,  if  tht 
rails  are  poorly  connected,  very  perceptible  flux  of  cur- 
rent from  the  track  to,  for  instance,  a  water  main  running 
parallel  to  it  and  but  a  few  feet  away.  Fig.  29  shows  this 
state  of  things.  Let  A  B  be  the  track  and  C  D  a  water 
main  half  a  dozen  feet  below  the  level  of  the  track.  The 
resistance  between  any  particular  points  of  A  B  and  C  D  is 
at  all  times  large,  owing  to  the  high  specific  resistance  of 
the  material  between  them,  but  the  area  between  A  B  and 
CD  in  a  long  stretch  of  track  is  so  great  that  if  the 


FIG.  28. 


fall  in  potential  in  A  B  is  not  very  slight  indeed,  there  will 
be  a  considerable  flow  of  current  into  and  along  C  D.  To 
take  a  concrete  example,  let  A  B  be  twenty  rods  long,  and 
suppose  C  D  to  be  a  foot  in  diameter  and  six  feet  distant 
from  AB.  The  total  area  of  material  in  direct  circuit 
would  probably  be  a  strip  100  metres  long  and  not  less  than 
a  metre  wide.  Such  a  strip  would  contain  a  million  square 
centimetres  area  and  we  then  have  to  compute  the  resist- 
ance of  a  block  of  bad  conductor  a  million  square  centi- 
metres in  section  and  perhaps  averaging  200  cm.  long. 
This  we  can  regard  as  built  up  of  a  million  strips,  each  one 
centimeter  square  and  200  cm.  long,  connected  in  parallel. 
The  total  resistance  would  then  be  the  resistance  of  one  such 
strip  divided  by  1,000,000.  In  fact  the  resistances  of 
these  elements  would  be  very  various  and  the  currents- 
•would  flow  in  all  sorts  of  irregular  lines,  but  we  are  deal 


40    POWER  DISTRIBUTION  FOR  ELECTRIC   RAILROADS. 

ing  here  only  with  the  average  result.  Suppose  the  ma- 
terial has  a  specific  resistance  of  a  thousand  ohms  per  cubic 
centimetre,  then  the  resistance  of  one  element  would  be 
200,000  ohms,  but  the  whole  mass  would  have  a  resistance 
of  only  one-fifth  of  an  ohm;  hence  if  there  should  be  between 
track  and  pipe  an  average  difference  of  potential  of  ten  volts, 
an  amount  sometimes  exceeded  in  real  cases,  there  would  be 
within  the  distance  considered  a  flow  of  fifty  amperes  be- 
tween track  and  pipe. 

As  large  pipes  may  weigh  several  hundred  pounds  per 
yard,  it  is  clear  that  their  conductivity  cannot  be  neglected, 
although  in  most  cases  it  has  no  noticeable  effect  on 
the  resistance  of  the  system.  In  any  case,  these  extra- 
neous metallic  conductors  cannot  properly  be  counted  as  a 

B 


e™^yc:'{^;;V^:V;.^ 

"  "  Street  Railway* Journal 

FIG.   29. 

part  of  the  circuit,  except  under  very  unusual  conditions, 
since  flow  of  current  to  them  is  highly  objectionable,  as 
will  presently  be  shown. 

To  sum  up  the  matter  of  earth  return,  properly  so 
called,  the  earth,  so  far  from  being  a  body  of  high  con- 
ductivity, useful  for  eking  out  the  carrying  power  of  the 
rail  return,  is,  for  most  useful  purposes,  to  be  regarded  al- 
most as  a  non-conductor.  Its  specific  resistance  is  so  high 
and  irregular  that  it  is  of  no  value  as  part  of  the  return 
circuit,  while  its  conducting  power  in  great  areas  comes 
into  play  only  in  an  unpleasant  and  troublesome  way.  The 
conduction  which  occurs  is  very  irregularly  distributed 
and  varies  greatly  from  time  to  time.  For  all  long  lines 
of  railroad  and  for  many  small  street  railway  systems,  the 
earth  may  be  left  entirely  out  of  account,  and  in  large 
street  railway  systems  it  is  generally  a  source  of  anxiety. 
In  the  early  days  of  electric  railroading  quite  the  opposite 
view  was  often  held  and  roads  were  constructed  accord- 


THE   RETURN   CIRCUIT.  41 

ingly.  In  reality  the  bonding  was  then  so  generally  ineffi- 
cient, that  probably  even  the  earth  may  have  -improved 
thergeneral  conductivity.  Experience  has  shown  that  the 
view  here  presented  is  generally  the  correct  one,  and  the 
realization  of.it  has  done-much  to  improve  general  prac- 
tice. Possibly  interference  with  telephone  circuits  did 
much  to  prolong  faith  in  the  earth  as  a  conductor,  but  the 
.telephone  deals  with  millionths  of  amperes,  which  are  quite 
insufficient  for  operating  street  cars. 

.  Recurring  to  Fig.  2Q,:and  granting  the  conditions  to 
be  such  that  a  current  flows  from  track  to  pipe  at  some 
point  in  the  system,  that  current  must  leave  the  pipe  and 
either  pass  back  to  a  part  of  the  track  having  a  lower  po- 
tential or  to  some  other  conductor  by  which  it  may  work 
its  way  back  towards  the  station. 

Now  wherever  an  electric  current  leaves  a  metallic  con- 
ductor for  one  which  owes  its  conductivity,  as  does  the 
earth,  to  the  presence  of  liquid,  the  surface  of  the  former 
is  corroded — gnawred  away  by  the  chemical  action  set  up 
by  the  current.  Hence  the  pipe  under  consideration  wrould 
soon  show  a  surface  pitted  with  rust,  and  eventually  the 
corrosion  would  extend  through  to  the  inner  surface  of  the 
pipe  and  start  a  leak.  Similarly  the  rails  are  corroded 
from  the  exit  of  the  current,  but  the  result  is  not  of  much 
consequence. 

This  matter  of,  electrolytic  corrosion  of  water  pipes, 
gas  pipes  and  other  buried  conductors  is  serious  in  very 
many  electric  railway  systems,  so  serious  that  it  is  worth 
detailed  study  as  one  of  the  gravest  factors  bearing  on  the 
design  of  the  return  circuit.  One  would  naturally  suppose 
that  the  actual  amount  of  damage  done  by  the  compara- 
tively small  currents  distributed  over  a  large  space,  would 
be  rather  slight.  So  it  would  be  if  it  were  intermittent, 
but  when  the  electrolytic  process  goes  steadily  on  week 
after  week  and  month  after  month,  the  aggregate  result  is 
somewhat  formidable.  One  ampere  flowing  steadily  from 
an  iron  surface  will  eat  away  very  nearly  twenty  pounds  of 
metal  per  year.  So,  in  the  case  of  conduction  to  a  pipe 


42     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

just  investigated,  the  resulting  corrosion  would  amount  to 
half  a  ton  per  year.  This  destruction  would  be  done  in  the 
surfaces  of  exit  from  the  pipe  and  if  the  conditions  were 
such  as  to  limit  these  surfaces  to  a  comparatively  small 
area  the  local  damage  would  be  very  serious. 

Klectrolytic  corrosion  of  underground  conductors  by 
stray  currents  was  first  noticed  in  the  case  of  lead  covered 
telephone  cables  in  Boston  by  I.  H.  Farnham,  to  whose 
researches  much  of  our  knowledge  of  the  subject  is  due. 

Lead  is  attacked  at  the  rate  of  about  seventy-five 
pounds  pet  ampere  per  year,  so  that  the  result  is  extremely 


LEAD  CABLE 

FIG.  30. 

marked.  Fig.  30  gives  a  diagrammatic  view  of  the  circuit 
through  such  a  cable.  Part  of  the  current  used  on  the 
railway  circuit  passes  from  the  rails  to  the  cable  and  thence 
along  it  to  the  neighborhood  of  the  motors,  where  it  passes 
back  to  the  track  and  the  moving  cars.  The  mischief  is 
done  at  this  point  and  not  while  the  current  is  flowing  in 
the  cable.  The  effect  produced  is  a  severe  corrosion  of  the 
leacj  covering  of  the  cable  taking  place  irregularly  upon 
the  surface  and  forming  pits,  which  may  penetrate  the 
sheath  and  destroy  the  insulation  of  the  cable. 

Investigation  showed  the  state  of  things  on  the  Boston 
system  to  be  very  interesting.  At  the  time,  the  positive 
poles  of  the  dynamos  in  the  power  station  were  connected 
with  the  rails  so  that  the  current  passed  into  them  and 


RETURN   CIRCUIT.  43 

thence  to  the  pipes  and  cables,  emerging  from  them  at  vari- 
ous points  in  the  system.  The  corrosion  was  thus  widely 
distributed,  but  from  local  conditions  of  conductivity  was 
most  apparent  in  spots.  Careful  measurements  of  the 
potential  between  the  track  and  the  cables  were  made  in  a 
large  number  of  places  with  the  result  shown  in  the  map 
(Fig.  31).  Near  the  power  stations  the  flow  was  from  track 
to  cables,  but  over  the  main  area  of  the  city  it  was  from 
cables  to  track,  giving  a  large  area  in  which  corrosion 
might  be  expected.  Differences  of  potential  as  high  as 


EAST 

BOSTON 


FIG   31. 

five  volts  were  observed,  while  experiments  in  other  cities 
have  shown  as  much  as  twenty-five  volts.  It  is  interest- 
ing to  note  that  one  of  the  first  experiments  tried  to  re- 
lieve this'  electrolytic  action  was  to  sink  in  the  earth 
ground  plates  connected  to  the  cables  in  the  hope  that 
the  current  flow  would  take  place  mainly  through  them. 
The  potential  differences  even  at  points  quite  near  these 
plates  were  practically  unchanged,  showing  very  plainly  the 
intense  badness  of  the  earth  as  a  conductor,  which  has 
already  been  pointed  out. 

The  method  of  treatment  which  proved  most  effective 
in  reducing  the  electrolytic  effects,  was  first  to  locate  the 


44     POWER   DISTRIBUTION   FOR    ELECTRIC    RAILROADS. 

trouble  as  nearly  as  practicable  in  definite  areas  and  then 
to  check  it  in  these  areas.  In  the  first  place  the  dynamo 
connections  were  reversed  so  that  the  stray  current  would 
enter  pipes  and  cables  over  the  most  of  the  system/but 
would  leave  them  en  route  for  the  negative  terminal  of  the 
dynamo  only  in  the  districts  immediately  surrounding  the 
power  houses.  Thus  it  would  be  certain  that  the  damage 
would  be  limited  to  known  areas  which  could  be  attacked 
locally  with  success,  instead  of  being  scattered  where  the 
trouble  would  be  hard  to  locate  and  -harder  to  remedy. 
Kven  within  these  areas  conduction  and  consequent  elec- 
trolysis is  likely  to  be  very  irregularly  distributed,  so  that 
serious  trouble  may  occur  at  one  point  when  points  near 
by  are  apparently  unaffected. 


FIG.  32. 

Fig.  32  shows  the  result  of  this  change.  The  ' '  danger 
areas ' '  shown  here  as  before  by  shading  on  the  map,  are 
comparatively  small,  although  within  them  the  differences 
of  potential  were  quite  as  great  as  before.  Now  the  prob- 
lem was  to  lead  the  current  back  to  the  dynamo  without 
compelling  it  to  leave  the  cables,  and  corrode  them  at  the 
points  of  exit.  To  this  end,  large  copper  conductors  were 
extended  through  the  danger  area  and  thoroughly  con- 
nected at  intervals  to  the  telephone  cables.  The  result 


THE   RETURN    CIRCUIT.  45 

was  excellent,  since  the  stray  currents,  instead  of  passing 
from  the  cables  through  the  earth  to  the  track,  took  the 
easier  path  through  the  supplementary  conductors. 

A  measurement  of  the  current  thus  collected  from  the 
telephone  cables  into  a  main  ground  wire  from  the  station 
showed  over  500  amperes  capable,  if  flowing  continuously, 
of  eating  away  37,500  Ibs.  of  lead  per  year.  And  as  this 
current  did  not  include  that  which  found  its  way  to  waiter 
and  gas  pipes,  the  real  amount  of  current  which  left  the 
rails  and  wandered  home  through  underground  conductors 
was  considerably  larger  than  the  figure  mentioned,  prob- 
ably several  times  as  great.  The  distribution  of  this  cur- 
rent is  so  irregular  from  place  to  place,  as  indicated  on  the 
map,  that  it  would  be  very  hard  indeed  to  estimate  the  total 
proportion  it  bears  to  the  whole  current  on  the  system. 
So  far  as  data  are  available  however  they  indicate  that  we 
would  not  be  wide  of  the  truth  in  saying  that  ten  to  twenty 
per  cent  of  the  current  on  the  system  may  follow  other 
paths  than  that  through  the  rails  and  bonds.  Even  more 
than  this  may  appear  in  occasional  instances.  So  while  the 
earth  helps  the  return  circuit  directly  but  little,  buried 
conductors  may  help  very  materially,  perhaps  to  their  own 
serious  detriment.  It  should  be  remembered  that  the  elec- 
trolytic action  is  not  necessarily  proportional  to  the  differ- 
ences of  potential  such  as  are  noted  on  the  maps.  The 
places  most  injured  depend  on  local  conductivity  and  some 
of  the  worst  instances  recorded  have  occurred  where  the 
measured  potential  difference  was  only  one  or  two  volts. 

Figs.  33  and  34  give  a  graphic  idea  of  the  kind  of 
damage  that  is  done  to  pipes  by  electrolysis  from  stray 
currents.  Fig.  33  shows  the  effect  of  corrosion  on  an  iron 
gas  pipe,  and  Fig.  34  that  on  a  lead  water  pipe.  Both  are 
from  photographs  of  the  ' '  horrible  examples. ' '  As  the 
action  tends  to  become  concentrated  in  spots,  a  pipe  may  be 
perforated  in  a  rather  short  time.  Iron  water  pipe  has  some- 
times been  riddled  in  five  to  eight  months.  That  this  is 
easily  possible  may  be  readily  seen,  for  suppose  that  con- 
ditions are  such  as  to  get  in  a  certain  spot  a  flow  of  half 


46     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

an  ampere  in  a  space  of  one  square  foDt.  Suppose  the  pipe  to 
be  $/%  in.  thick,  therefore  weighing  about  twenty-five  pounds 
per  square  foot  of  surface.  If  the  electrolytic  action  were 
perfectly  uniform  the  pipe  would  be  reduced  to  an  unsub- 
stantial shell  in  a  single  year,  and  since  the  corrosion  al- 
ways shows  irregular  pits  the  pipe  would  almost  infallibly 
be  perforated  in  six  months.  Very  curious  differences 


FIG.  33, 

exist  between  electrolytic  actions  in  various  situations, 
depending  on  the  chemical  conditions  in  the  soil.  Some- 
times the  action  produces  a  thick  dense  coating  of  ordinary 
rust  which  almost  suspends  the  electrolytic  process,  while 


FIG.  34, 

elsewhere  the  products  of  decomposition  are  more  soluble, 
and  the  work  goes  on  until  the  iron  is  eaten  away  leaving 
a  mere  shell  of  the  contained  carbon  and  electrolytic  debris 
generally. 

It  is  worth  while  to  note  that  surface  protection  of 
pipes  by  painting  with  asphalt  and  the  like  has  been  shown 
by  the  Boston  experience  to  be  practically  worthless,  as 
the  corrosion  seems  to  work  under  the  film,  which  can  never 
be  made  really  insulating  to  any  useful  extent. 


THE   RETURN   CIRCUIT.  47 

In  spite  of  the  quite  perceptible  assistance  that  may 
be  rendered  by  underground  pipes  to  the  general  conduc- 
tivity of  the  return  system,  every  effort  should  be  made  to 
avoid  it.  For,  even  if  the  various  lines  of  pipe  are  protect- 
ed by  the  supplementary  wire  method  described,  there 
may  be  electrical  differences  at  the  joints  of  the  pipes  quite 
sufficient  to  cause  local  corrosion  in  serious  amount.  Joints 
in  water  pipe  are  better  mechanically  than  electrically  and 
the  currents  flowing  through  them  may,  as  we  have  seen, 
be  rather  heavy.  Take  for  example  Fig.  35.  Suppose 
that  owing  to  oxidized  and  dirty  surface  of  contact  the 
joint  A  has  a  resistance  of  .005  ohm  and  that  a  current  of 
one  hundred  amperes  is  flowing  through  it  in  the  direction 
indicated  by  the  arrow.  The  fall  of  potential  through  the 
joint  would  then  be  .5  volt,  lines  of  current  flow  would  be 
set  up  as  shown  by  the  dotted  lines  and  a  ring  of  corrosion 
B  C  would  be  set  up  on  the  positive  side  of  the  joint.  Half 
a  volt  is  quite  enough  to  do  the  work,  and  though  the 
action  might  be  slow  it 
would  be  sure.  In  point  ///-" 


of  fact  the  lead  calked  joints 

used   in    wrater    pipe    may 

readily   show   a    resistance 

ten   or   twenty   times   that 

just     assumed,    sometimes 

even   an   ohm   or   more,   a  ^^y 

case  still  more  serious.  pIG>  35< 

Therefore  all  conduction 

by  pipes  ought  to  be  avoided  as  faf  as  possible  unless  they 
are  electrically  continuous.  Even  if  they  are,  protection 
by  supplementary  wires  is  somewhat  risky  since  while  it 
may  relieve  trouble  in  the  conductors  so  connected  it  may 
enhance  the  danger  to  neighboring  pipes  not  thus  protected. 
Joints  between  pipes  of  different  materials  are  espe- 
cially dangerous,  for  instance  between  cast  iron  and  cement 
lined  sheet  iron.  Under  exceptionally  unfavorable  condi- 
tions joints  have  been  eaten  out  in  as  short  a  time  as  six 
weeks. 


48      POWER  DISTRIBUTION   FOR  ELECTRIC   RAILROADS 

Liberal  use  of  supplementary  wires  has  great  use 
as  an  emergency  measure,  applied  to  systems  already 
existing,  but  here,  as  generally,  an  ounce  of  prevention 
is  worth  a  pound  of  cure.  The  proper  return  circuit  of 
the  railway  should  be  made  so  good  that  the  stray  currents 
shall  be  quite  negligible,  and  all  methods  of  palliating  their 
evil  effects  should  be  considered  secondary  in  importance 
and  to  be  shunned  rather  than  courted.  It  must  not  be  un- 
derstood that  these  methods  are  condemned,  for  they  may 
be  of  much  use,  but  they  should  be  employed  only  to  deal 
with  the  residual  currents  after  they  have  been  reduced  to 
the  lowest  practicable  terms  by  means  of  improving  the 
track  circuit. 

The  main  point  of  such  improvement  lies  in  the  con- 
nections between  rail  and  rail.  If  the  resistance  of  the 
bonds  and  their  contacts  were  negligible  there  would  be 
very  trifling  stray  currents. 

For  example,  if  we  are  dealing  with  a  double  track  of 
ninety- pound  rail,  the  resistance  is  about  -g^  ohm  per 
thousand  feet  or  .0087  ohm  per  mile.  Such  a  structure 
could  carry  1000  amperes  with  a  loss  of  but  8.7  volts 
per  mile  and  should  reduce  the  stray  currents  to  a  very 
minute  percentage  since  the  resistance  is  not  only  very 
small  compared  with  any  probable  value  of  the  earth 
resistance  between  track  and  pipes,  but  also  very  small 
compared  with  the  resistance  of  the  pipes  themselves  in- 
cluding their  bad  joints.  With,  say,  one  per  cent  of  the 
current  in  the  earth  conductors  the  electrolytic  action, 
while  not  absolutely  suppressed,  would  be  so  slow  and  so 
trifling  as  to  be  scarcely  worth  considering  save  at  a  few 
points  which  could  be  protected  if  necessary. 

All  this  points  to  the  necessity  of  the  most  perfect 
bonding,  as  before  pointed  out.  All  sorts  of  devices  have 
been  tried.  Two  of  the  most  ingenious,  aside  from  those 
already  referred  to,  consist  respectively  of  a  plastic  con- 
ducting film  squeezed  between  the  bond  surface  and  the  rail 
surface,  and  of  a  heavy  copper  dowel  pin  driven  into  a  hole 
in  the  end  of  one  rail  and  the  other  rail  forced  upon  it  and 


THE   RETURN   CIRCUIT.  49 

held  with  the  fishplate.  The  uncertain  point  about  these 
as  about  many  other  bonds  is  their  ability  to  endure  jarring 
and  corrosion.  Bonds  are  sometimes  subject  to  the  sam? 
sort  of  electrolytic  action  just  mentioned  in  connection  witb 
pipe  joints.  Lately  many  bonds  have  been  electrically 
brazed  to  the  rails  by  a  process  closely  akin  to  electric 
welding.  The  amount  of  power  required  is  only  15  to  20 
K.  w.  and  in  point  of  low  resistance  and  permanence  the 
result  is  exceedingly  good. 

The  most  radical  cure  for  joint  resistance  of  rails  may 
be  found  in  the  two  now  familiar  processes  for  making 
continuous  rails.  That  a  continuous  rail  is  entirely  feasi- 
ble mechanically  now  admits  of  no  dispute.  Expansion 
does  not  and  cannot  take  place  longitudinally  when  rails 
are  firmly  embedded  in  paving,  even  under  the  extremes  of 
temperature  encountered.  Whatever  yielding  there  is,  is 
lateral,  and  the  track  is  not  thrown  out  of  line. 

The  electrically  welded  joint  when  carefully  made  is 
strong  and  reliable  and  of  almost  infinitely  small  resistance. 
The  contact  is  non-corrodible,  of  great  surface  and  so  in- 
timate as  not  sensibly  to  increase  the  resistance  of  the 
track.  It  is  as  far  superior  to  a  bond  contact  as  the  latter 
is  to  the  contacts  made  through  rusty  fishplates.  A  track 
so  excellent  mechanically  and  electrically  needs  no  com- 
mendation here,  more  than  to  reiterate  the  value  of  a  com- 
plete and  permanent  connection  between  rails.  Unfortu- 
nately the  simplest  form  of  joint  which  has  shown  ample 
strength  is  the  butt  welded  form  which  requires  energy  to 
the  amount  of  200  H.  p.  or  more,  a  quantity  not  often 
readily  attainable.  Recently  a  very  good  and  reliable  form 
of  joint  has  been  made  by  welding  on  a  pair  of  fish  plates 
at  each  joint  the  union  not  being  over  the  whole  surface, 
but  at  three  large  and  heavy  bosses  so  distributed  as 
to  make  a  solid  and  rigid  joint  This  form  of  weld 
takes  much  less  current  than  a  butt  weld  and  is  amply 
strong. 

The  ' '  cast  welded  ' '  joint  has  now  come  into  very  con- 
siderable use  Mechanically  it  is  superior,  but  electrically 


50      POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

it  is  scarcely  the  equivalent  of  the  welded  joint.  Between 
these  two  rival  continuous  rail  processes  it  is  difficult  to 
choose  Certainly  both  afford  at  once  the  solution  for  the 
joint  alignment  and  the  bonding  difficulties.  The  ' '  cast 
welded  '  joint  is  by  far  the  more  widely  used  on  account 
of  its  great  mechanical  strength  and  the  ease  with  which 
it  is  made.  Both  are  likely  to  come  into  very  extensive 
use  in  large  city  roads  where  the  electrolytic  troubles  are 
usually  most  noticable,  although  small  roads  are  not 
exempt  from  them.  The  resistance  of  a  cast  welded 
joint,  although  not  uniformly  negligible,  is  about  the 
same  as  that  of  the  very  best  bonded  joints  and  is  quite  as 
permanent. 

It  has  often  been  urged  that  a  double  trolley  system 
should  be  employed  to  avert  danger  of  electrolytic  action. 
Experience  has  shown  that  the  double  trolley  is  not  likely 
to  become  a  favorite  with  street  railway  men.  It  can  be 
worked  successfully  with  proper  care,  but  the  mechanical 
difficulties  in  the  way  of  installing  and  keeping  up  the 
overhead  system  of  frogs,  crossings  and  the  like  are  some- 
what formidable.  On  a  straightaway  road  with  no 
branches  or  few  the  task  is  easier,  but  for  the  purpose  in 
hand  such  roads  are  not  the  ones  requiring  the  most  serious 
consideration.  The  troubles  belong  especially  to  compli- 
cated city  systems  in  which  the  difficulties  of  a  double 
trolley  system  are  something  terrific.  Inasmuch  as  every 
electric  railway  company  has  to  pay  for  what  can  be  made 
a  magnificent  return  circuit,  it  seems  totally  needless  to 
throw  away  the  rails  and  operate  a  double  metallic  circuit 
overhead.  Especially  is  this  true  in  view  of  the  fact,  that 
considerations  of  track  stability  and  durability  point  to  the 
use  of  the  continuous  rail  which  minimizes  at  the  same  time 
the  electrical  difficulties. 

It  must  be  remembered  that  in  long  distance  lines  such 
as  are  found  in  interurban  and  similar  work,  the  use  of 
continuous  rails  is  liable  to  cause  trouble  from  insufficient 
resistance  to  expansion,  as  such  roads  generally  are  exposed 


THE   RETURN   CIRCUIT.  51 

to  more  violent  changes  of  temperature.  On  the  other 
hand,  in  the  case  of  such  roads  trouble  from-  electrolytic 
action  is  usually  relatively  small  or  entirely  absent,  so  that 
bonding  is  sufficient.  Also  as  will  be  explained  later,  in 
these  roads  for  heavy  service  and  rather  high  speed  there 
may  sometimes  be  good  reason  for  using  two  trolleys,  quite 
aside  from  all  questions  of  good  return. 

Of  course,  when  the  alternating  current  motor  is  thor- 
oughly developed  for  railway  service  much  of  the  danger  of 
electrolysis  will  be  escaped,  whatever  the  character  of  the 
return  circuit,  but  there  will  still  exist  every  reason  for 
making  the  rail  return  as  perfect  as  possible  from  motives 
of  economy  alone.  For  when  bad  bonding  can  increase 
the  total  resistance  of  the  track  circuit  ten  or  a  dozen  times, 
as  has  happened  many  times,  the  waste  of  energy  due  to 
the  increased  drop  in  the  circuit  is  burdensome. 

For  example,  take  a  single  track  of  ninety  pound  rail 
10,000  ft.  long.  With  continuous  rails  the  resistance  per 
thousand  feet  would  be  ^ J7  of  an  ohm  and  for  the  whole 
distance  .033.  With  200  amperes  flowing,  the  drop  would 
be  6.6  volts  and  the  loss  of  energy  more  than  one  kilowatt. 
Now  suppose  each  bond  contact  with  its  half  of  the  bond 
wire  to  have  a  resistance  of  .001  ohm.  On  each  line  of 
rail  there  would  be  660  of  these  so  that  the  total  bond  re- 
sistance of  the  track  would  be  .33  ohm  and  the  drop  due 
to  this  bond  resistance  with  a  current  of  200  amperes 
would  be  66  volts.  The  corresponding  loss  of  energy 
would  be  13.2  k.  w.  more  than  enough  to  operate  an 
extra  car.  At  the  cost  of  power  generally  found  this  waste 
would  represent  in  the  vicinity  of  $1000  per  year  net  loss,  a 
pretty  high  price  to  pay  for  the  privilege  of  having  a  poorly 
connected  track,  liable  to  cause  serious  trouble  from  stray 
currents.  And  this  instance  represents  not  at  all  an  ex- 
tremely bad  case,  but  a  very  common  one. 

The  moral  of  all  this  is  that  just  as  much  care  should 
be  spent  on  the  joints  underground  as  on  those  overhead, 
in  fact  more,  since  the  latter  are  but  slightly  liable  to  cor- 
rcsion  while  the  former  run  great  risk  of  it.  For  this 


52     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

reason  the  continuous  rail  is  doubly  desirable  since  it  not 
only  avoids  constant  loss  of  energy  in  the  rail  joints,  but 
averts  a  rather  heavy  cost  of  maintenance.  With  continu- 
ous rails  some  cross  bonding  may  be  desirable  to  give  se- 
curity against  breaks,  but  it  comes  into  use  only  in  emer- 
gencies. -Next  to  the  continuous  rail  the  best  construction 
employs  rails  of  some  of  the  recent  deep  sections,  rolled  in 
60  ft.  lengths.  These  are  laid  with  long  fish  plates  at  the 
joints  secured  with  twelve  heavy  bolts,  and  are  double 
bonded  at  each  joint.  A  track  so  constructed  has  only 
half  the  usual  number  of  joints,  thus  halving  the  usual 
resistance  due  to  the  bonding.  These  long  rails  are  rather 
un wieldly  as  they  weigh  1800  to  2000  Ibs.  each,  but  their 
use  is  very  advantageous. 

To  prevent  electrolytic  destruction  of  neighboring  con- 
ductors by  stray  current  from  the  rails  the  best  simple  ad- 
vice that  can  be  given  is  as  folV>ws: 

1 .  Use  the  continuous  rail  system ;  or 

2.  Bond  very  thoroughly;  put  the  positive  pole  of  the 
dynamo  on  the  overhead  line;  join  the  negative  directly  to 
the  track  without  intentional  earth  connection,  and 

3.  In  any  case  investigate  the  potential  between  track 
and  buried  conductors  and  run  supplementary  wires  from 
these  conductors  to  the  dynamo  if  necessary. 

This  applies  to  small  systems  as  well  as  large.  The 
only  cases  which  may  be  fairly  excepted  are  electric  roads 
running  through  country  where  there  are  no  buried  con- 
ductors near,  and  elevated  roads  which  are  really  a  special 
case  of  the  double  trolley  system.  As  electric  railways 
have  become  more  common  and  more  thoroughly  under- 
stood the  conditions  of  the  return  circuit  have  been  much 
ameliorated,  but  sins  against  Ohm's  law  are  still  distress- 
ingly common.  A  feeling  still  seems  to  be  rife  that  what 
is  concealed  from  the  eye  may  be  scamped,  as  when  the 
guileful  wiring  contractor  runs  underwriters'  wire  through 
the  ceilings  and  puts  okonite  at  the  joints.  It  is  bad 
enough  for  a  dishonest  contractor  to  do  that  sort  of  thing, 
but  what  shall  we  say  of  a  man  who  cheats  himself  by 


RETURN   CIRCUIT.  53 

doing  poor  work  on  his  return  circuit  without  even  the  ex- 
cuse of  economy. 

We  are  now  in  a  position  to  determine  the  quantity 
which  was  the  ultimate  object  of  this  investigation  into  the 
details  of  the  return  circuit;  i.e.,  its  total  net  value  as  a 
conductor  compared  with  the  outgoing  circuit. 

This  is  obviously  not  a  fixed  quantity  in  either  abso- 
lute or  relative  value,  for  even  neglecting  joint  resistances 
there  is  far  less  difference  between  the  weights  of  the  rail 
used  in  various  systems  than  between  the  weights  of  over- 
head copper.  An  ordinary  electric  road  uses  perhaps  a  rail 
of  seventy  pounds  per  yard.  A  single  track  so  constituted 
is,  neglecting  joints,  of  conductivity  equal  to  2,200,000 
c.  m.  of  copper.  If  the  rails  were  continuous  it  is  clear 
enough  that  in  a  road  of  small  or  moderate  size  they  would 
be  perhaps  ten  times  as  good  a  conductor  as  the  overhead 
system.  This  would  allow  for  a  No.  o  trolley  wire  and  a 
No.  oo  main  feeder  on  the  average  all  over  the  line.  On 
the  other  hand,  taking  the  resistance  of  bonds  and  joints  as 
double  that  of  the  rail  itself,  the  equivalent  of  the  rail  in 
copper  falls  to,  say,  733,000  c.  m.,  which  is  less  than  four 
times  the  overhead  system  just  assumed.  If  this  system 
averaged  a  No.  ooo  feeder,  plus  the  trolley  wire,  it 
would  have  almost  exactly  three  times  the  resistance  of  the 
track  circuit. 

In  large  systems  the  rails  often  run  as  high  as  ninety 
pounds  per  yard,  so  that  a  single  track  would  be  equal 
to  3,000,000  c.  m.  of  copper.  With  continuous  rails 
this  full  equivalent  could  be  taken,  but  the  feeder  area 
plus  a  No.  oo  trolley  wire  would  hardly  be  less  than  750,- 
ooo  c.  m.,  so  that  the  resistance  of  the  overhead  wiring 
would  be  about  four  times  that  of  the  track.  More  com- 
monly, making  the  same  allowance  for  bonds  as  before,  the 
track  equivalent  would  be  1,200,000  c.  m.  and  the  trolley 
and  feeder  copper  would  have  only  about  one  and  a  half 
times  the  track  resistance.  Not  infrequently  the  bonding 
is  imperfect  enough  to  reduce  the  track  equivalent  to  900,- 
ooo  c.  m.,  which  would  frequently  be  equaled  or  ex- 


54     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 


ceeded  by  the  trolley  and  feeder  copper,  raising  the  ratio  to 
equality.  A  double  track,  of  course,  improves  matters.  We 
may  tabulate  these  results  somewhat  as  follows,  calling  R  1 
the  track  resistance  and  R  the  overhead  resistance. 

R1  =  .1  to  .2  R.  Exceedingly  good  track  and  very 
light  load. 

Ri  =  .2  to 


Ri  ==  .2  to 


3  R.     Good  track  and  moderate  load. 

,6  R.     Fair  track,  moderate  load. 

3  R.     Exceptional  track  and  large  sys- 


tem. 


Ri  ==  .3  to    .7  R. 
RI  =  .7  to  i.o  R. 


Good  track,  large  system. 
Poor  track,  large  system. 
In  cases  now  somewhat  exceptional  the  track  resist- 
ance may  exceed  the  overhead  resistance  considerably.  The 


Drop-Volts 

§  8 

"v 

^ 

*X 

^v 

^ 

Vs 

"V,, 

X, 

ot, 

*s 

^ 

tf 

^. 

^ 

f 

^ 

X 

-V 

^ 

^N 

^ 

^X 

V^ 

Return  circuit 

FIG.  36. 

Street  Railway  Journal 

assumption  now  frequently  made,  that  the  track  resistance 
is  one- quarter  that  of  the  overhead  system  really  repre- 
sents a  better  state  of  things  than  usually  exists.  To 
justify  it  requires  the  combination  of  continuous  rail  or 
exceptionally  perfect  bonding,  with  conditions  of  load  that 
do  not  require  large  feeder  capacity.  Under  the  ordinary 
conditions  R1  =  .4Ris  probably  nearer  the  truth.  The 
proportion  between  R  and  R1  has,  of  course,  a  very  im- 
portant bearing  on  the  design  of  the  overhead  system.  If 
the  return  circuit  had  no  resistance  then  the  entire  drop 


THE   RETURN    CIRCUIT. 


55 


\vould  take  place  in  the  overhead  conductors  and  we  could 
calculate  the  line  for  any  given  drop  by  the  simple  formula 


e.   m.  = 


with  D  for  the  linear  single  distance.  Bearing  in  mind 
however  the  resistance  of  the  return  circuit,  it  is  evident 
that  for  a  given  total  loss  in  volts  more  copper  must  be 
placed  overhead  than  would  be  necessary  if  the  return  cir- 
cuit were  of  zero  resistance.  In  other  words,  if  we  are 
confronted  by  a  considerable  loss  in  this  return  circuit  it  is 
necessary  to  have  proportionately  less  elsewhere  in  the 


100 


treet  Railway  Journal 


37- 


circuit.  With  no  resistance  in  the  return  circuit  the  drop 
in  voltage  may  be  represented  graphically  by  Fig.  36. 
Here  the  whole  drop  is  in  the  outgoing  circuit  which  can 
consequently  be  rather  small.  If,  on  the  other  hand,  we 
take  the  actual  case  in  which  the  return  circuit  has  a  very 
perceptible  resistance,  the  distribution  of  the  drop  will  be 
as  in  Fig.  37,  which  is  given  by  R1  =  .43  R.  This  means 
that  to  preserve  the  same  conditions  of  total  loss  in  the 
circuit  the  overhead  copper  must  be  increased  by  forty- 
three  per  cent,  since  of  the  total  100  volts  to  be  lost  it  is 
now  permissible  to  lose  but  70+  in  the  outgoing  circuit. 
Hence  to  take  account  of  loss  in  the  return  circuit  the 
formula  just  given  must  be  Altered  by  changing  the  co-i- 


56     POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

slant  in  accordance  with  the  new  conditions,  which  are 
there  actually  found  in  practice.  The  proper  amount  of 
increase  in  the  constant  is  a  little  uncertain  as  is  indicated 
by  the  table  just  given.  For  R1  =  .4  R  however  the  con- 
stant is  14.4  so  that  we  may  rewrite  the  copper  formula  as 
follows: 

14.4  CD 
c.  m.  =  —  I—  r  -  . 

In  the  vast  majority  of  cases  the  constant  will  lie  be- 
tween 14  and  15.  The  exact  value  to  be  assumed  depends 
on  the  conditions  as  to  track  circuit  and  load  in  the  par- 
ticular case  considered,  and  can  be  judged  approximately 
from  the  table.  It  may  sometimes  be  desirable  to  make  a 
few  trial  calculations  with  different  constants  in  order  to 
get  a  clear  idea  of  the  possible  amount  of  copper. 

It  is,  of  course,  possible  to  determine  a  condition  for 
minimum  cost  of  the  conducting  system,  taking  account  of 
the  cost  of  copper,  rails  and  bonding,  but,  generally  speak- 
ing, the  rail  is  fixed  by  purely  mechanical  considerations 
while  there  are,  as  has  been  shown,  good  reasons  for  making 
the  track  circuit  thoroughly  good.  In  applying  the  above 
formula,  as  we  shall  in  the  next  chapter,  it  should  be  re- 
membered that  in  extensive  systems  the  constant  may  have 
to  be  modified  in  passing  from  one  locality  to  another,  for 
the  rail  conditions  will  probably  vary  and  the  load  condi- 
tions most  assuredly  will  change. 

In  cases  where  the  track  return  is  not  used,  as  in 
double  trolley  and  conduit  roads,  the  outgoing  and  return 
leads  may  or  may  not  be  duplicates  of  each  other.  If  the 
total  drop  were  equally  divided  between  them  the  feeder 
formula  would  of  course  become  the  familiar 


E 

and  the  return  would^  have  the  same  area  and  total  weight 
as  the  feeder  system  thus  determined.  Ordinarily  there 
would  be  little  advantage  in  making  the  two  sides  of  the 
circuit  equal  and  the  designer  would  be  guided  mainly  by 


THE   RETURN   CIRCUIT. 


57 


2000 


1200 


600 


200 


REA  OF  COPPER  REQUIRED  FOR  DELIVERING 
100  AMPERES  UP  TO  30000'  ) 

1000  AMPERES  UP  TO  3000')  

AT  10  TO  50  VOLTS  LOSS.   UPPER  SCALE 

EADS  TO  3000'BY  50rPER  SQUARE.    LOWER 

READS  TO  30000  BY  500'PER  SQUARE 


15 

DISTANCE 


PLATE  II. 


58      POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

convenience.  Often  the  easiest  procedure  mechanically  is 
to  install  one  or  more  heavy  return  cables  for  o  predeterm- 
ined fraction  of  the  total  drop  and  to  compute  the  feeder 
system  precisely  as  if  dealing  with  a  track  return.  For 
the  greatest  economy  in  copper  a  particularly  careful  study 
of  the  probable  distribution  of  the  load  should  be  made. 
Of  course,  one  may  divide  the  drop  between  feeder  system 
and  return  in  almost  any  convenient  way,  subject  to  the 
limitation  imposed  by  danger  of  overheating,  without 


COPPER  EQUIVALENT 

OF 
STEEL  RAILS 

FOR 

SPECIFIC  CONDUCTIVITIES 
FROM  9  TO  15?b  OF  THAT    OF  COPPER 


POUNDS  PER  YARD 

PLATE  III. 


.120 


affecting  the  economy  of  the  distribution,  but  when  one 
deals  with  a  track  return  of  uniform  section  which  must 
be  installed  and  paid  for  anyhow,  there  is  less  need  of 
refinement  than  in  using  costly  cables. 
»  Probably  the  best  method  of  design  in  these  cases  is 
to  follow  the  general  procedure  to  be  found  in  the  subse- 
quent chapters,  but  with  close  attention  to  the  limits  and 
variations  of  load  in  the  various  sections  of  the  line,  not 
adhering  closely  to  anything  like  a  track  constant,  but 
taking  the  data  for  feeders  and  return  out  of  Plate  II  with 
such  division  of  the  total  drop  between  them  as  seems 
expedient  from  the  standpoint  of  simplicity  in  overhead  or 


THE   RETURN   CIRCUIT.  59 

conduit  construction.  Plate  II  is  merely  an  extension  of 
Plate  I,  p.  7,  arranged  with  reference  to  heavy  work  of 
this  class,  the  abscissae  being  the  total  lengths  of  the  wire 
under  consideration  and  not  the  lengths  of  the  circuits  as 
in  Plate  I. 

In  case  the  working  conductors  are  of  other  material 
than  copper  they  should  be  reduced  to  the  equivalent 
section  of  copper.  For  this  purpose  Plate  III,  developed 
from  Fig.  17,  p.  30,  will  be  found  convenient  in  all  com- 
putations involving  rails  or  other  iron  or  steel  conductors. 

Third  rail  systems  with  ordinary  track  return  may  or 
may  not  involve  supplementary  feeders.  Plates  II  and  III 
will  enable  these  cases  to  be  easily  computed,  once  the 
loads  are  determined. 


CHAPTER   III. 

DIRECT   FEEDING   SYSTEMS. 

By  direct  feeding  is  meant  the  supply  of  current  to 
the  working  system  of  conductors  from  a  single  central  sta- 
tion, without  any  intermediary  apparatus.  It  is  the  system 
employed  on  most  present  electric  street  railroads,  save  a 
few  of  the  largest  size.  It  is  ordinarily  used  on  interurban 
lines  and  would  be  universally  applied  were  there  not  many 
cases  in  which  the  distribution  of  power  from  a  single 
station  becomes  uneconomical  at  any  practicable  voltage 
on  account  of  the  great  distances  involved. 

Nearly  all  interurban  lines,  and  especially  the  systems 
which  are  likely  to  result  from  the  conversion  of  steam  into 
electric  lines,  can  be  best  operated  by  other  means  which 
will  be  described  in  subsequent  chapters.  Indeed  a  care- 
ful examination  of  very  many  existing  electric  railways 
will  disclose  the  fact  that  direct  feeding  is  being  worked 
far  beyond  its  proper  limits  of  application  and  is  the  cause 
of  serious  pecuniary  loss,  both  in  interest  on  a  huge  invest- 
ment in  copper  and  in  power  needlessly  lost  on  the  line. 

Direct  feeding  however  is  properly  applied  in  most  in- 
stances, and  must  be  ultimately  applied  as  the  distributing 
system  almost  universally,  since  even  where  substations  are 
employed  the  lines  proceeding  from  them  are  often  a  case 
of  direct  feeding  and  must  be  treated  as  such. 

Electric  railway  feeding  systems  are  akin  in  principle 
to  those  employed  in  simple  cases  of  distribution  for  light- 
ing, and  yet  in  practice  differ  from  them  very  radically  in 
certain  particulars.  Railway  feeders  are  not  generally  de- 
signed to  preserve  uniform  voltage  within  the  area  fed, 
but  to  hold  the  voltage,  admittedly  variable,  within  certain 
rather  wide,  but  fixed  limits.  Lighting  feeders  must  be  de- 
signed with  reference  to  a  load  varying  in  the  same  area 


DIRECT   FEEDING   SYSTEMS.  6T 

from  time  to  time,  but  yet  closely  confined  to  that  area; 
railway  feeders  must  be  so  designed  as  to  meet  not  only  a 
load  variable  in  amount  from  second  to  second,  but  shifting 
from  place  to  place  obedient  to  causes  that  follow  no  definite 
law.  On  the  other  hand  not  only  are  railway  feeders 
absolved  from  the  necessity  of  holding  the  voltage  closely 
uniform,  but  by  virtue  of  this  they  can  the  more  easily  be 
arranged  to  meet  extreme  shifting  of  the  load. 

In  early  electric  railways  the  trolley  wire  proper  was 
rather  small  and  the  feeding  was  often  relatively  quite  as 
complex  as  that  in  large  modern  systems. 

The  conditions  which  must  be  met  in  planning  a  direct 
feeding  system  are  roughly  as  follows: 

1.  The  maximum  fall  in  voltage  at  any  point  in   the 
system  under  all  working  conditions  must  not   exceed  a 
fixed  amount. 

2.  The  average   drop  throughout  the  system  under 
normal    conditions  must    equal   a    certain  predetermined 
amount. 

3.  The  feeders  must  be   so  connected  that  accidents 
to  the  working  conductors  shall  interfere  with  traffic  to  as 
small  an  extent  as  possible. 

To  meet  these  various  conditions  a  large  number  of 
arrangements  of  feeders  have  been  devised,  many  of  which 
are  in  extensive  use.  The  following  are  some  of  the  most 
usual,  which  have  stood  the  test  of  experience. 

i .  The  so-called  ladder  system  shown  in  Fig.  38.  Here 
one  pole  of  the  dynamo  is  earthed  as  usual  and  the  other 
is  connected  to  the  trolley  wire  C  D,  and  also  to  the  feeder 
A  B.  These  are  connected  at  intervals  of  a  few  hundred 
feet  by  subfeeders  a,  b,  c,  d,  e,f,  etc.,  which  are  generally 
hardly  more  than  tie  wires  uniting  the  principal  feeder  to 
the  trolley  wire.  This  arrangement  was  very  common  in 
early  electric  roads.  It  made  possible  the  use  of  a  very 
slender  trolley  wire  merely  large  enough  to  carry  conven- 
iently the  current  for  cars  running  between  the  subfeeders, 
and  made  the  system  tolerably  free  from  interruption  by 
accidents  to  the  trolley  wire,  which  from  its  small  size  was 


02     POWER    DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

rather  prone  to  break.  Both  the  trolley  wire  and  the 
principal  feeder  are  continuous  and  of  uniform  cross  sec- 
tion. This  continuity  is  useful  in  case  of  the  crowding  of 
cars  at  one  or  more  points  on  the  line  since  it  brings  to  the 
rescue  the  full  conductivity  of  the  system.  It  is  bad  how- 
ever in  case  of  short  circuits  in  that  the  main  circuit 
breaker  at  the  station  is  quite  likely  to  open  and  stop 
every  car  on  the  line. 

As  a  real  feeding  system  it  hardly  deserves  the  name, 
since  electrically  it  is  nothing  more  than  a  continuous 
working  conductor  of  uniform  area.  The  properties  of 
such  a  conductor  have  already  been  fully  considered  in 
Chap.  i.  The  only  additional  fact  that  has  to  be  taken 
into  account  in  the  ladder  system  is  the  limited  conductivity 
of  the  trolley  wire  between  the  subfeeders.  The  drop  in 
voltage  at  a  car  located  at  any  point  is  practically  the  drop 


Street  Ry.  Journal      D 

FIG.  38. 

in  the  principal  feeder  up  to  that  point  plus  the  drop  in  the 
trolley  wire  from  the  car  to  the  nearest  subfeeders,  which 
are  virtually  in  parallel,  inasmuch  as  current  flows  into  the 
trolley  in  both  directions  along  the  trolley  wire. 

2.  A  system  similar  in  some  respects  to  Fig.  38  is 
shown  in  Fig.  39.  Here  there  is  as  before  a  principal 
feeder  A  B.  The  trolley  wire  C  D  is  not  however  contin- 
uous, but  is  broken  by  insulating  joints  into  separate 
sections  of  approximately  equal  length  each  with  its  own 
subfeeder  a ,  b,  c,  etc.  The  added  conductivity  of  the  con- 
tinuous trolley  wire  is,  of  course,  sacrificed  by  this  arrange- 
ment. Both  the  trolley  and  feeder  are  generally  of  uniform 
area  throughout  their  respective  lengths  and  the  system  is 
electrically,  to  all  intents  and  purposes,  a  uniform  linear 
conductor  save  for  the  abrupt  change  in  conductivity  in 
passing  from  the  principal  feeder  to  any  subfeeder  and  its 
section  of  trolley  wire.  As  regards  a  load  at  any  poin- 


DIRECT   FEEDING  SYSTEMS.  63 

the  total  drop  is  that  in  the  principal  feeder  up  to  the  sub- 
feeder  controlling  the  section  in  question  plus  the  drop  in 
the  subf  eeder  and  the  trolley  wire  up  to  the  load. 

The  advantage  gained  by  cutting  the  trolley  wire  into 
short,  independent  sections  is  a  certain  amount  of  immunity 
from  breakdowns.  The  subfeeders  ay  b,  cy  etc.,  are  usually 
provided  with  fuses  or  switches  or  both,  so  that  while  in 
case  of  a  break  in  the  trolley  wire  the  cars  on  the  adjacent 
sections  are  not  deprived  of  current  any  more  than  in  the 
ladder  system,  there  is  no  longer  the  danger  of  stopping 
traffic  by  blowing  fuses  at  the  station,  since  the  subf  eeder 
fuse  immediately  acts  to  stop  an  excessive  flow  of  current. 
In  addition,  in  case  of  fire  or  flood  affecting  any  part  of 
the  system,  the  disturbed  region  can  be  very  promptly 
isolated  by  opening  the  circuit  at  the  subfeeders.  In  cities 


o 

Street  Ry.  Journal 


FIG.  39. 


where  fires  are  of  frequent  occurrence  such  an  arrangement 
is  highly  necessary,  although  it  is  generally  desirable  to  use 
a  far  more  complete  feeding  system  in  connection  with  it. 
Both  the  arrangements  just  shown  are  entirely  without 
special  provisions  for  holding  up  the  voltage  at  distant 
parts  of  the  line,  depending  practically  on  the  conductivity 
of  the  principal  feeder. 

3.  A  true  feeding  system  corresponding  in  a  general 
way  with  Fig.  38  is  shown  in  Fig.  40.  Here  A  JB  is  the 
trolley  wire  while  in  multiple  with  it  are  feed  wires 
tapped  into  the  trolley  wire  at  a,  b  and  c.  These  feeders 
are  generally  quite  independent  of  each  other  up  to  their 
respective  junctions  with  the  trolley  wire.  A  load  at  any 
point,  as  d,  receives  its  current  in  both  directions  through 
the  trolley  wire,  which  in  turn  draws^current  from  the  ad- 
jacent feeders.  The  conductivity  available  at  the  load  d  is 
that  of  the  trolley  wire  from  A  to  d,  reinforced  by  the  feed- 
ers a  and  b\  in  parallel  with  that  of  the  trolley  wire  section 


64     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

from^to  c  and  the  feeder  c.  With  the  arrangement  of  Fig. 
40  it  is  quite  possible  to  hold  the  voltage  fairly  uniform  by 
giving  sufficient  area  to  the  longer  feeders.  As  a  matter  of 
convenience,  to  avoid  the  undue  multiplication  of  wires,  the 
distances  A  a,  ad,  etc.,  between  feeders  are  made  consider- 
ably longer  than  in  the  ladder  system:  hence  the  trolley 
wire  is  generally  larger.  Of  course,  it  must  be  large  enough 
to  avoid  excessive  drop  in  the  sections  b  d  and  c  d  when 
load  is  applied  at  d.  As  a  rule  the  distances  A  a,  ad,  etc., 
are  several  thousand  feet  except  where  the  traffic  is  very 
heavy.  With  No.  o  or  No.  oo  trolley  wire  the  distance 
named  is  not  generally  excessive.  As  compared  with  the 
ladder  distribution  this  one  has  the  great  advantage  of  giv- 
ing a  fairly  uniform  voltage,  and  can  be  more  readily  ar- 
ranged to  handle  abnormal  loads  at  distant  parts  of  the 


-B 


, 

Street  Ry.  Journal 


FIG.  40. 


line.  It  has  also  the  same  convenient  property  of  giving 
current  to  each  car  from  two  directions  so  as  to  minimize 
the  effect  of  breaks  in  the  trolley  wire.  It  is  however  ex- 
posed to  trouble  in  case  of  serious  short  circuits,  and  is  in- 
convenient in  the  matter  of  cutting  out  portions  to  execute 
considerable  changes  in  wiring  or  to  avert  accident. 

4.  An  obvious  modification  of  the  arrangement  just 
mentioned  is  that  shown  in  Fig.  41.  This  bears  the  same 
relation  to  (3)  that  (2)  does  to  (i).  It  shares  with  (3) 
the  advantage  of  maintaining  fairly  constant  voltage  under 
normal  conditions,  though  it  is  somewhat  at  a  disadvantage 
in  case  of  a  heavy  load  on  a  distant  section,  since  that  sec- 
tion must  depend  on  its  own  feeder  alone  without  assist- 
ance from  adjacent  sections.  The  feeders  a,  b,  c,  etc.,  are 
provided  with  individual  switches  and  cut-outs  at  the  station 
so  that  if  a  short  circuit  occurs  nothing  worse  can  happen 


DIRECT   FEEDING  SYSTEMS.  65 

than  the  temporary  disabling  of  that  particular  section, 
while  if  necessity  demands  any  section  can  be  promptly  cut 
out  of  circuit  in  case  of  fire  along  the  line  or  any  other 
sufficient  cause.  (4)  is  very  well  adapted  for  use  on  long 
lines  with  fairly  regular  traffic.  L,ike  (3)  it  requires  a 
rather  heavy  trolley  wire  for  the  best  results.  A  load  at 
any  point  is  supplied  by  the  feeder  for  that  section  in 
series  with  the  trolley  wire  between  the  load  and  the  feeder 
junction,  so  that  the  drop  under  any  given  conditions  is 
very  readily  computed. 

In  both  (3)  and  (4)  it  is  sometimes  convenient  to  tie 
two  or  more  feeders  together,  as  shown  by  the  dotted  line 
at  d  (Fig.  41).  This  procedure  reinforces  the  conduc- 
tivity with  reference  to  the  section  thus  connected,  as  b} 
and  while  it  may  lower  the  voltage  of  sections  beyond  the 


1 

d 

f 

.                   r                       1 

A           A              a                             b                             c 

Street  Ry.  Journal 

Fic.  41. 

link,  is  very  useful  when  a  particular  section  is  exposed  to 
severe  loads  from  grades  or  massing  of  cars,  particularly 
since  such  linking  can  be  applied  at  any  time  that  the 
service  may  require  it. 

In  very  many  cases  it  is  advantageous  to  install  a  com- 
posite feeding  system  which  can  be  made  in  a  considerable 
measure  to  unite  the  advantages  of  those  already  described. 
A  very  useful  combination  is  that  shown  in  Fig.  42. 

Here  the  trolley  wire,  AB,  is  cut  into  sections  of  vary- 
ing length,  short  where  considerable  danger  of  interruption 
of  service  exists,  long  where  longer  sections  can  be  more  con- 
veniently utilized.  C  is  a  principal  feeder  as  in  the  ladder 
system  connected  at  a  and  b  to  a  continuous  trolley  line, 
and  at  c,  d  and  e  to  trolley  sections.  This  principal  feeder 
is  reinforced  by  feeders  K  and  F  to  equalize  the  voltage 
more  perfectly  in  the  region  of  dense  traffic,  while  the  inde- 


66    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

pendent  feeeders,G  and  H,  supply  the  long  isolated  sections, 
/and^-.  G  and  H  are  moreover  linked  at  f  if  the  condi- 
tions of  service  require.  Fig.  42  represents  the  actual 
arrangement  of  an  extensive  feeding  system  much  more 
closely  than  any  of  the  simpler  arrangements  shown.  As 
a  matter  of  fact  such  a  complex  system  is  generally  the  out- 
growth of  the  conditions  which  develop  in  service  rather 
than  the  result  of  deliberate  forethought.  Nevertheless, 
good  engineering  often  demands  the  adoption  of  such  ap- 
parently complex  methods. 

In  general,  independent  feeders  are  necessary  to  pre- 
serve good  working  pressure  in  outlying  districts  where 
comparatively  independent  lines  are  worked,  while  in  re- 


L 

Street  Ry.  J< 

I 
urnal 

| 

c 

1               1 

•6      '       ' 

J  1  1  1 
C             (f.             e        .     j 

V             a              6 

FIG.  42. 

gions  of  dense  traffic  the  tendency  is  to  link  together  the 
principal  feeders  of  neighboring  lines  into  a  network  rein- 
forced by  special  feeders  wherever  necessary.  The  trolley 
wire  is  sectionalized  only  in  so  far  as  danger  from  fires  and 
electrical  troubles  require.  Although  a  continuous  trolley 
wire  is  now  far  less  necessary  than  formerly  on  account  of 
improved  methods  of  construction,  on  the  other  hand  an 
extensive  subdivision  into  sections  hinders  the  full  use  of 
all  the  copper  installed  and  increases  the  danger  of  local 
stoppage  of  traffic.  On  any  railway  system,  street  or  other, 
continuity  of  service  is  of  the  first  importance,  both  by 
reason  of  the  direct  loss  from  suspension  of  traffic  and  the 
indirect,  but  far  more  serious,  loss  of  public  confidence  and 
'goodwill. 

Consequently  it  is  often  advisable  to  take  chances  in 
order  to  keep  running,  and  linking  feeders  and  trolley  into 
a  continuous  system  to  drive  through  a  time  of  short  cir- 


DIRECT   FEEDING  SYSTEMS.  67 

cuit  if  possible  rather  than  shut  down  part  of  the  system. 
The  present  tendency  is  to  make  the  various  sections  of 
feeders  and  trolley  wire  separable  rather  than  separate,  so 
that  they  can  be  cut  apart  when  absolutely  necessary,  but 
not  long  before  that  crisis. 

IvOng  lines,  interurban  and  the  like,  may  often  be  best 
treated  indirectly  through  substations,  but  when  direct 
feeding  is  employed,  it  is  ordinarily  best  to  use  a  very  sub- 
stantial trolley  wire,  not  smaller  than  No.  oo,  installed  in 
separable  but  not  disconnected  sections,  and  supplied  with 
current  by  separate  feeders,  which  may  be  linked  if  local 
conditions  require.  If  large  power  units  are  to  be  em- 
ployed, requiring  large  currents,  it  is  better  to  use  a  very 
large  trolley  wire  than  to  install  a  principal  feeder,  since 
with  large  currents  the  larger  the  contact  surface  of  the 
working  conductor  the  better,  and  the  conductivity  of  the 
trolley  wire  can  be  relieved  if  insufficient  by  connecting 
each  section  to  its  feeder  in  several  places  instead  of  one. 
There  is  no  reasori  however  why,  on  large  work  such  as  is 
found  in  converting*  steam  roads  to  electric,  the  working 
conductor  may  not  have  a  cross  section  equivalent  to  No. 
oooo  wire  or  more  which  enables  comparatively  long  sections 
between  feeders  to  be  employed  with  advantage.  For  ex- 
ample, suppose  a  No.  oooo  trolley  wire  carrying  a  current 
of  200  amperes  per  section  received  equally  from  the  two 
adjacent  feeders.  This  condition  would  be  met  by  a  train 
requiring  one  hundred  kilowatts  to  drive  and  located  mid- 
way between  two  feeders.  Allowing  no  more  than  two 
per  cent  loss,  i.  e. ,  about  ten  volts  in  the  trolley  wire  be- 
tween feeder  junction  and  load  and  substituting  the  above 

values  in   the  fundamental  equation  c.   m.  —  II  ,  the 

distance  between  feeders  should  be  about  4000  ft.  Inas- 
much as  the  average  drop  produced  by  the  moving  train, 
with  a  maximum  of  two  per  cent  midway  between  feeders, 
would  be  but  one  per  cent,  it  would  generally  be  advisable 
to  increase  this  amount.  Allowing  an  average  drop  of  two 
per  cent  in  the  trolley  wire,  i.  e. ,  a  maximum  of  four  per 


68     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

cent,  the  proper  distance  between  feeders  would  be  virtu- 
ally doubled,  rising  to  about  8000  ft. — a  mile  and  a  half. 

For  long  roads,  then,  one  may  use  with  advantage 
such  an  arrangement  of  feeders  as  is  shown  in  Fir;.  43. 

Here  a  continuous  heavy  trolley  wire  is  divided  into 
sections  of,  say,  a  mile  to  a  mile  and  a  half  in  length,  each 
with  a  junction  to  the  feeding  system.  This,  as  shown, 
consists  of  three  main  feeders,  each  supplying  two  sections 
of  trolley  wire.  The  number  of  these  main  feeders  and 
the  number  of  sections  each  supplies  is  regulated  by  con- 
venience and  local  conditions,  as  is  too  the  length  of  each 
section.  The  sketch  (Fig.  43)  shows  merely  the  principle, 
which  is  well  suited  to  roads  up  to  a  dozen  miles  in  length 
fed  from  somewhere  near  the  middle.  Such  roads  are  apt 


Street  Ry.  Journal 

FIG.  43-        * 

to  require  rather  large  units  of  loads,  due  to  well  loaded 
trains  and  high  speed,  but  the  number  of  trains  to  be  oper- 
ated at  any  one  time  is  usually  small.  A  rather  nice 
question  sometimes  arises  as  to  the  relative  cross  section  of 
copper  to  be  put  in  the  trolley  wire  and  in  the  feeders.  In 
the  large  work  that  we  are  just  now  considering,  the  trolley 
wire  must  be  in  any  event  large  enough  to  give  sufficient 
contact  with  the  trolley.  And  this  is  apt  to  indicate  about 
as  large  a  working  conductor  as  can  conveniently  and  se- 
curely be  supported.  Therefore  the  feeders  will  be  rela- 
tively smaller  than  in  ordinary  street  railway  practice,  and 
it  is  not  advantageous  to  separate  permanently  the  sections 
of  trolley  wire,  thus  throwing  away  the  conductivity  of  its 
large  cross  section.  Whenever  double  tracks  are  used  it 
goes  quite  without  saying  that  the  whole  system  of  con- 
ductors should  be  united,  each  trolley  wire  serving  as  a 
feeder  to  the  other. 


DIRECT   FEEDING  SYSTEMS.  69 

Occasionally,  too,  on  single  track  roads  with  frequent 
turnouts,  two  trolley  wires  are  strung"  ten  or  twelve  inches 
apart,  each  to  accommodate  the  cars  running  in  one  direc- 
tion, so  as  to  entirely  avoid  overhead  switches  of  any  kind. 
This  arrangement  is  shown  in  Fig.  44,  and  while  it  is  not 
now  very  widely  used,  it  is  exceedingly  convenient  in  cer- 
tain cases.  In  Fig.  44  the  track  at  a  turnout  is  shown  by 
the  solid  lines  and  the  two  trolley  wires  by  dotted  lines. 
The  trolley  wire,  A  B,  would  naturally  be  used  by  cars  run- 
ning from  right  to  left  as  indicated  by  the  arrow,  while  C  D 
would  be  used  by  cars  running  from  left  to  right.  Each 
car  keeps  to  its  own  trolley  wire  throughout  the  track,  un- 
less it  is  necessary  to  change  over  in  backing  around  a 
turnout.  This  double  trolley  device  enables  long  exten- 
sions to  be  handled  without  feeders. 


- — o 


• Street  Ry.  Journal 

FIG.  44. 

Before  passing  to  the  actual  computation  of  a  trolley 
and  feeder  system,  we  must  go  back  to  our  two  f funda- 
mental propositions  and  inquire  into  the  permissible  maxi- 
mum drop  and  what  we  mean  by  average  drop. 

Suppose  that  ten  per  cent  average  drop  has  been  de- 
cided upon  in  a  given  case, — What  is  really  meant  by  this? 
There  has  been  considerable  confusion  on  this  point.  Are 
we  to  understand  that  this  average  drop  is  that  determined 
from  the  effect  of  the  maximum  working  load  throughout 
the  system,  or  is  it  the  average  loss  on  the  parts  of  the  sys- 
tem considered  separately  irrespective  of  their  relative 
amounts.  Is  it  the  drop  produced  by  the  average  load  or 
the  average  of  the  drops  produced  by  the  simultaneous 
loads  at  some  particular  time? 

To  reduce  the  matter  to  a  common  basis  with  other 
cases  of  the  electrical  transmission  of  energy,  we  are  at  lib- 


70    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

erty  to  put  but  one  interpretation  upon  average  drop.  By 
it  we  should  mean  in  every  case  that  a  certain  specified 
proportion  of  the  energy  delivered  to  the  line  during  a  par- 
ticular period  is  to  be  lost  in  the  transmission.  On  this  basis 
we  can  design  the  system  for  conditions  of  maximum  econ- 
omy, knowing  approximately  the  probable  cost  of  energy 
per  kilowatt  hour  and  the  price  of  copper.  Starting  with 
this  definition,  we  can  then  intelligently  work  out  the  re- 
lation of  this  average  energy  loss  to  the  loss  in  volts  at  the 
various  parts  of  the  system.  It  is  necessary  however  to 
bear  in  mind,  first,  that  the  same  conditions  of  economy 
with  respect  to  loss  in  transmission  do  not  necessarily  hold 
for  all  parts  of  a  given  system,  and  second,  the  question  of 
economy  in  transmission  is  quite  subordinate  to  that  of 
successful  operation. 

As  regards  the  former  consideration,  the  average  energy 
delivered  to  an  electric  railway  system  is  a  very  different 
thing  from  either  the  maximum  energy  or  the  average 
energy  during  the  hours  of  heavy  load.  The  load  factor, 
i.  e. ,  the  ratio  between  average  and  maximum  output  on  a 
railway  system  is  generally  rather  unsatisfactory,  as  has  al- 
ready been  indicated.  It  ranges  in  general  from  .3  to  .6, 
varying  greatly  with  the  size  of  the  system,  the  character 
of  the  service  and  the  habits  of  the  people  who  ride.  In 
cities  many  interesting  facts  appear  from  the  load  curve 
of  an  electric  railway — the  movements  of  workingmen, 
the  crowd  of  shoppers  going  downtown  in  the  forenoon, 
the  migration  in  the  early  afternoon,  the  homegoing  at 
six  and  the  theatre  crowd  an  hour  and  a  half  later.  All 
these  factors  of  load  operate  with  varying  force,  not  only  in 
different  places,  but  in  different  parts  of  the  same  system. 
The  changes  from  day  to  day  are  considerable,  but  on  the 
whole  the  same  line  preserves  its  character  remarkably 
well.  The  result  of  a  varying  load  factor  is  a  necessary 
limitation  in  the  permissible  loss  of  energy.  For  if  we 
have  a  load  factor  of  .3,  the  average  loss  of  energy,  what- 
ever economy  of  transmission  may  indicate  must  not  be 
enough  to  cause  at  maximum  load  a  drop  in  voltage  suffi- 


DIRECT  FEEDING  SYSTEMS.  71 

cient  to  interfere  with  the  proper  operation  of  the  cars.  If 
we  write  for  the  maximum  permissible  drop,  V,  v  for  the 
drop  corresponding  to  the  loss  of  energy  for  greatest  econ- 
omy of  transmission,  for  the  load  factor,  I,,  and  for  the  drop 
assumed,  V1,  we  have  the  following  inequality  which  sets 
a  limit  of  drop  which  must  not  be  exceeded 

V^<^LV 
Very  fortunately  it  usually  happens  that 

s;<Z,  V 

so  that  there  is  no  special  difficulty  in  making  Vi  =  v. 
But  it  is  not  safe  to  assume  this  happy  condition  of  things 


.12    1 


FIG.  45. 


Stre  t  Ry,  Journal 


without  some  investigation.  It  may  be  true  of  one  part  of 
the  system  and  not  of  another.  It  is  necessary  therefore  to 
look  into  the  various  parts  separately  in  laying  out  any  con- 
siderable system.  Fig.  45  shows  three  load  curves  which 
may  be  supposed  to  be  from  three  parts  of  the  same  system, 
together  with  the  summation  curve  of  the  three  from  which 
the  total  load  factor  would  be  determined.  I  may  be  taken 
as  the  load  curve  of  a  main  urban  system,  while  curves  II 
and  III  will  serve  for  branches.  IV  is  the  summation 
curve  of  the  whole.  The  load  factor  of  this  final  curve  is 
very  evidently  worse  than  that  of  the  main  line,  curve  I, 
since  heavy  loads  in  morning  and  evening  on  branches  II 
and  III  raise  the  morning  and  evening  maximum  values 


72     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

on  IV.  The  load  factor  of  II  is  hardly  better  than  .3 
while  that  of  I  is  nearly  .6.  Consequently  we  have  far 
less  latitude  in  planning  the  conductors  for  this  branch 
than  in  case  of  the  main  line,  being  always  confronted  by  a 
high  maximum  to  be  taken  care  of.  The  load  factor  how- 
ever does  not  fully  represent  the  precautions  that  have  to 
be  taken.  It  shows,  to  be  sure,  the  normal  maxima,  but  it 
does  not  include  the  effect  of  shifting  load. 

This  is  really  a  very  serious  matter  in  making  the 
plans  for  a  conducting  system  and  the  probabilities  of  the 
case  need  to  be  carefully  weighed.  A  base  ball  park,  for 
instance,  located  far  out  on  a  branch  line  means  trouble  un- 


FIG.  46. 

less  it  be  taken  into  account.  It  means  that  now  and  then, 
not  only  all  the  regular  cars  on  the  line,  but  all  the  extras 
that  can  be  spared,  will  be  massed  at  or  near  the  distant  end 
of  the  branch  and  brought  in  heavily  loaded  and  all  to- 
gether. It  is  the  same  effect  that  would  be  obtained  from 
a  steep  grade,  except  that  it  is  only  occasional.  The  amount 
of  such  an  extra  load  may  be  sufficient  to  double  the  ordi- 
nary maximum  load  and  that  in  the  most  disadvantageous 
place,  i.  e. ,  at  the  end  of  the  line.  From  what  has  been  said 
it  is  sufficiently  evident  that  laying  out  the  conductors  for 
a  large  system  is  more  a  matter  of  acute  judgment  than  of 
exact  theory. 

The  reason  for  this  is   that   there  are   no  data   suffi- 
cient to  justify  a  general  theory  based  upon  them.     The 


DIRECT  FEEDING  SYSTEMS.  73 

value  of  the  load  on  an  electric  railway  is  so  uncertain, 
whether  for  any  stated  time  or  during  any  interval,  and  so 
uncertain  in  position  as  well  as  amount,  that  the  success  of 
any  calculation  depends  almost  wholly  on  the  skill  with 
which  the  data  are  assumed. 

A  convenient  way  of  entering  upon  the  calculation  of 
a  conducting  system  is  to  take  up  the  data  involved  in  the 
following  consecutive  steps. 

1.  Extent  of  lines. 

2.  Average  load  on  each  line. 

3.  Center  of  distribution. 

4.  Maximum  loads. 

5.  Trolley  wire  and  track  return. 

6.  General  feeding  system. 

7.  Reinforcement  at  special  points. 

The  first  two  steps  are  necessary  preliminaries  to  the 
third.  The  fourth  determines  the  permissible  drop,  the 
fifth  gives  the  division  of  the  overhead  copper  between 
trolley  and  feeders,  and  the  allowance  that  must  be  made 
for  the  resistance  of  the  return  circuit.  The  sixth  stage  is 
the  preliminary  calculation  of  the  conductors  and  the 
seventh  the  modification  of  this  to  take  full  account  of  local 
conditions.  The  application  of  the  whole  process  is  best 
shown  by  working  out  an  Irypothetical  system  in  detail, 
step  by  step.  Two  cases  may  properly  be  taken  up;  first 
a  regular  street  railway  system,  and  second,  an  inter  urban 
line  of  moderate  length. 

Suppose  a  new  system  is  to  be  installed  or  an  old  one 
reorganized  of  which  the  track  is  shown  in  the  simple  chart 
(Fig.  46).  Here  the  main  line,  A  B  C  D,  is  double  track 
throughout.  A  B  is  10,000  ft.,  B  C  2000  and  C  D  4000, 
making  a  total  length  of  16,000  ft.  At  #  C  the  main  line 
is  joined  by  the  single  track  branch,  C  K,  10,000  ft.  long, 
on  which  at  F  G  is  a  five  per  cent  grade  2000  ft.  long. 

Step  i.  Lay  out  the  track  to  scale,  noting  the  dif- 
ferent distances  carefully  and  the  extent  and  position  of 
grades.  The  scale  need  not  be  large,  say,  an  inch  to  the 
thousand  feet,  and  a  couple  of  tracings  of  the  chart  will 


74      POWER   DISTRIBUTION   FOR    ELECTRIC   RAILROADS. 

prove  convenient.  If  any  extensions  are  contemplated,  as 
at  E  H,  dot  them  in  as  they  will  enter  into  subsequent  cal- 
culations. As  shown,  K  H  is  supposed  to  be  5000  ft. 
Now  divide  the  road  into  sections  so  that  in  each  one  of 
them  the  service  shall  be  under  ordinary  conditions  fairly 
constant.  For  example,  the  main  double  track  would 
present  tolerably  uniform  conditions  throughout  and  could 
be  considered  as  a  single  section.  Owing  to  the  change  in 
direction  at  B,  however,  which  might  conceivably  affect 
the  location  of  the  power  station,  it  is  better  to  take  A  B  as 
one  section  and  B  D  as  a  separate  one.  C  E,  the  long 
single  track  branch,  will  naturally  form  a  third  section; 
while  H  E  may  be  taken  tentatively  as  a  fourth. 

Step  2.  Now  as  to  the  loads  upon  each  section.  The 
number  of  cars  on  a  road,  of  course,  depends  entirely  on  the 
traffic.  With  the  advantage  of  a  good  population  to  draw 
upon,  such  a  line  as  we  are  considering  might  operate  as 
many  as  twenty  motor  cars.  These  would  naturally  be  six- 
teen or  eighteen  foot  single  truck  cars,  probably  the  latter. 
We  may  then  assume,  say,  ten  such  cars  on  section  A  B, 
six  on  B  D  and  four  on  C  E.  Those  on  C  E  in  the  natural 
course  of  events  would  run  quite  independently,  simply 
serving  their  own  line.  We  can  then  assume  as  the  total 
load  twenty  eighteen  foot  cars,  each  equipped  with  a  pair 
of  standard  motors,  such  as  are  usually  rated  at  twenty- 
five  horse  power  each.  The  power  required  to  operate 
these  cars  is,  of  course,  exceedingly  dependent  on  the 
density  of  the  traffic.  So  long  however  as  the  cars  are 
equally  loaded  the  center  of  gravity  of  the  system  is  quite 
independent  of  the  absolute  amount  of  horse  power  re- 
quired for  each  car.  Recurring  now  to  the  theorems  re- 
garding center  of  gravity  in  Chap.  I,  we  are  in  a  position 
to  determine  the  best  position  for  the  power  station.  The 
only  question  to  be  first  decided  is  what  is  to  be  done 
with  respect  to  the  proposed  extension.  If  it  is  installed 
as  an  extension  of  C  E,  probably  two  additional  cars  would 
be  needed. 

Step  3.  As  the  service  on  each  section  is  uniform  the 


t  UNIVERSITY 
XPA- 


DIRECT   FEEDING  SYSTEMS. 


75 


a=io 


u  =•  6 


load  can  be  considered  as  concentrated  at  the  middle  point  of 
each  section.  Determining  the  center  of  gravity  of  the  three 
existing  sections  by  Fig.  47,  constructed  like  Fig.  10,  we 
find  this  center  at  e.  Combining  with  this  the  effect  of  the 
proposed  extension,  it  appears  that  the  addition  of  this 
extra  load  would  shift  the  center  of  gravity  to  e1,  a  dis- 
tance of  somewhat  less  than  500  ft.  Transferring  these 
points,  to  Fig.  46  we  have  the  theoretical  location  for  the 
power  station. 

Its  practical  location  is,  however,  a  very  different  mat- 
ter. Very  many  things  besides  cost  of  copper  for  distribu- 
tion enter  into  the  problem.  In  the  first  place  e  may  fall 

in  a  locality  in  which 
real  estate  is  very  valu- 
able, so  that  it  will  pay 
to  shift  the  center  of 
distribution  a  consider- 
able distance  rather  than 
endure  the  cost  of  a  site 
for  the  power  station  at 
e.  Again  e  may  be  in- 
convenient with  respect 
to  coal  and  water  sup- 
ply. The  cost  of  carting 

coal  or  pumping  the  water  for  condensation  purposes  may 
very  easily  outweigh  the  saving  in  copper  due  to  distribu- 
ting from  the  theoretical  point.  It  will  perhaps  be  found 
that  there  is  a  considerable  region  within  which  the  station 
can  profitably  be  shifted  to  obtain  cheap  land,  coal  and 
water.  It  is  not  difficult  to  form  an  idea  of  the  extent  of 
this  region.  To  do  so,  however,  we  need  an  approximate 
idea  of  the  cost  of  copper  for  distributing  the  necessary 
power  from  the  point  e.  ,/This  is  very  quickly  obtained. 
We  can  consider  a  load  of  s*xfen  cars  as  concentrated  at  a 
(Fig.  47).  This  is  approximately  3500  ft.  f rom  e.  Sim- 
ilarly six  cars  are  at  b,  5000 ft.,  and  four  cars  at  e,  3000 ft. 
We  have  seen  in  studying  Fig.  10  that  the  total  weight  of 
copper  required  for  such  a  system  is 


FIG.  47. 


76     POWER    DISTRIBUTION    FOR   ELECTRIC   RAILROADS. 


Remembering  that  we  are  considering  feed  wire  alone,  since 
the  trolley  wire  is  fixed  in  location,  we  may  assume  a  reason- 
able drop  in  voltage  of,  say,  thirty  volts.  K  above  then 
becomes  ff 

Forming  the  above  summation  we  have  at  twenty  am- 
peres per  car, 

2  W  =  ((10  x  20)  x  12.25 
-f-  6  X  20  X  25 
4-4  x  20  x  Q)  11  =  6787  Ibs. 

Now  at  fifteen  cents  per  pound  this  feeder  copper  would 
cost  just  about  $1000.  For  any  other  point  than  e  the 
cost  will  be  greater  by  varying  amounts  and  the  increase 
is  about  the  same  for  all  points  equidistant  from  e.  As  the 
weight  of  copper  varies  with  the  squares  of  the  distances, 
the  mean  distance  of  the  load  with  respect  to  weight  of 
copper  is  determined  by 

L3  C=^l3  <r=6i7o  where  C  =  2  c=^oo 
Hence  L  =  3950  ft.  nearly.  This  distance  is  the  radius  oi 
the  circle  about  which  the  station  can  be  shifted  without 
more  than  doubling  the  cost  of  copper  noted  above. 
That  is,  the  station  can  be  located  anywhere  within  about 
three-quarters  of  a  mile  of  the  center  of  gravity  of  the 
system  without  increasing  the  cost  of  copper  more  than 
$1000.  Such  figures  are  necessarily  approximate  only, 
since  in  practice  wires  cannot  be  run  in  straight  lines,  but 
have  to  follow  the  streets,  nevertheless  they  give  valuable 
information. 

A  brief  examination  of  proposed  sites  for  the  power 
house  will  generally  disclose  that  which  is  most  advanta- 
geous with  respect  to  coal  and  water,  and  a  quick  summa- 
tion as  above  will  tell  quite  nearly  whether  the  extra  cop- 
per will  cost  too  much  or  not.  In  the  case  before  us  we 
will  assume  the  point/  (Fig.  46)  as  best  meeting  all  the  re- 
quirements. As  the  distance  e  e1  is  small  compared  with 
the  displacement  of  /,  we  can  let  the  extension  question 
take  care  of  itself  and  are  ready  to  proceed  to 

Step  4.  The  predetermination   of   the   maximum   or 


DIRECT  FEEDING  SYSTEMS.  77 

average  load  is  no  easy  matter,  yet  upon  it  depends  the 
proper  design  of  the  conducting  system.  It  is  not  diffi- 
cult to  estimate  with  a  fair  degree  of  accuracy  the  actual 
power  which  must  be  supplied  to  drive  a  car  of  assumed 
weight  over  a  certain  line  at  a  given  speed.  But  what  the 
real  weight  of  the  loaded  car  will  be,  and  what  the  condi- 
tion of  the  line  wrill  be  is  a  case  at  best,  for  educated  guess- 
ing. Roughly  speaking  the  power  required  at  the  car 
wheel  for  a  speed  of  eight  miles  per  hour  is  .4  h.  p.  per 
ton,  plus  .4  h.  p.  per  ton  for  each  per  cent  of  grade.  More 
exactly 


Wherein  G  is  the  per  cent  grade,  W  the  weight  of  car  and 
contents  in  tons  and  P  the  total  horse  power.  This  assumes  a 
straight  track  and  a  tractive  effort  of  twenty  pounds  per  ton 
on  the  level.  But  there  are  always  some  curves,  the  speed  is 
often  above  eight  miles  per  hour  and  at  low  speeds  the 
motors  are  somewhat  less  efficient  than  at  high  speeds.  Al- 
lowing a  complete  efficiency  of  two-thirds  from  trolley  to 
car  wheel  and  assuming  a  pressure  at  the  car  of  about  500 
volts  we  shall  not  go  far  wrong  in  reckoning  i  j£  amperes 
per  ton  of  car  plus  i  %  amperes  per  ton  for  each  per  cent  of 
grade.  This  average  indicates  an  average  of  about  fifteen 
amperes  per  car.  The  average  current  taken  while  the 
car  is  under  full  headway  will  frequently  exceed  this 
amount,  but  an  allowance  of  fifteen  amperes  average 
throughout  the  hours  of  running  will  generally  be  nearly 
right  for  a  road  such  as  that  under  consideration.  With 
long  double  truck  cars  the  average  current  will  rise  to 
about  twenty  -five  amperes.* 

Now  the  maximum  current  must  be  considered.  On 
large  systems  it  may  be  no  more  than  twice  the  average. 
As  the  number  of  cars  becomes  smaller  this  ratio  in- 
creases. With  one  or  two  cars  it  is  no  uncommon 
thing  to  find  maximum  currents  of  four  or  five  times  the 
average.  Still  larger  ratios  would  be  common  if  the 
same  speed  were  maintained  on  grades  as  on  the  level 

*  A  good  average  rule  for  power  is  100  watt  hours  per  ton  of  car  per  mile  of 
schedule  epeed  per  hour. 


78    POWER  DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

portion  of  the  t  nek.  We  can  now  go  back  to  Fig.  46  and 
form  a  tolerably  ciear  idea  of  the  current  to  be  furnished. 
On  section  I,  A  B,  we  may  fairly  count  on  a  normal  load  of 
150  amperes,  rising  to  occasional  maxima  of,  say,  450  am- 
peres. On  section  2,  preserving  about  the  same  ratio  since 
it  is  really  a  continuation  of  section  i,  we  may  expect 
about  90  amperes  average  and  270  maximum.  On  section 
3  with  four  cars  the  average  wrould  be  about  60  amperes 
and  the  maximum  about  150  amperes.  These  figures  how- 
ever do  not  tell  the  whole  story,  for  they  give  no  clue  to 
the  points  at  which  the  maximum  currents  must  be  fur- 
nished. This  matter  depends,  of  course,  on  local  conditions. 
On  sections  i  and  2  it  is  quite  writhin  the  range  of  possi- 
bility to  have  all  the  cars  on  either  track  piled  up  at  either 
end  of  the  line  under  unfavorable  conditions.  We  should 
then  be  prepared  for  handling  a  load  of  not  less  than  half 
the  maximum  at  the  ends  of  the  sections,  and  preferably 
more  than  this.  On  a  very  large  system  it  is  quite  out  of 
the  question  for  all  the  maximum  load  to  be  concentrated 
at  one  end  of  the  line,  but  on  a  small  road  there  is  a  much 
greater  chance  of  such  a  contingency.  It  certainly  would 
not  be  safe  to  allow  for  less  than  300  amperes  at  the  ends 
of  section  i,  and  about  250  on  section  2. 

With  section  3  the  case  may  be  still  different.  Sup- 
pose we  have  a  base  ball  park  at  E  (Fig.  46).  To  handle 
the  crowds  comfortably  or  at  all  would  probably  require 
massing  about  K  fully  double  the  normal  number  of  cars 
on  the  branch  and  having  them  all  heavily  loaded  at  once, 
and  what  is  worse  starting  them  all  about  the  same  time. 
300  amperes  is  little  enough  to  allow  even  with  careful 
handling  of  the  cars  with  respect  to  starting. 

We  may  now  tabulate  our  currents  about  as  follows: 

Sect,  i  Sect.  2  Sect.  3. 

Average  150  90  60 

Normal  maximum  450  270  150 

Extraordinary  maximum 
at  end  of  section  300  250  300 

The  maximum  for  the  whole  road  would  probably 
seldom  or  never  exceed  750  amperes,  since  the  conditions 


DIRECT  FEEDING  SYSTEMS.  79 

which  produce  maximum  loads  seldom  operate  all  over  the 
system  at  once. 

With  these  data  we  can  attack  the  feeder  problem  after 
deciding  on  the  amount  of  copper  to  be  put  into  the  trol- 
ley wire  and  the  value  to  be  assigned  to  the  track  return. 

Step  5.  How  large  ought  the  trolley  wire  to  be?  The 
answer  to  this  question  must  be  somewhat  empirical,  but 
we  can  get  a  line  on  it  by  considering  the  currents  it  has  to 
carry.  Adopting  the  ladder  system  of  Fig.  38  a  very  small 
trolley  wire  would  answer.  But  we  have  seen  that  this 
arrangement  is  of  little  service  in  equalizing  the  voltage 
along  the  line,  and  hence  it  is  better  on  the  whole  to  use 
the  system  of  Fig.  41  or  some  modification  of  it.  To  avoid 
running  an  inconvenient  number  of  feeders  it  is  then  de- 
sirable to  install  a  trolley  wire  big  enough  to  carry  current 
for  the  service  of  a  considerable  distance.  Referring  now  to 
Plate  i,  page  8,  we  see  that  allowing  a  drop  of  five  per  cent, 
i.e.,  twenty-five  volts,  in  the  trolley  wire,  all  that  should 
generally  be  tolerated  at  normal  load,  we  can  get  reason- 
ably long  distances  between  feeding  points,  say  3000  ft.  or 
more,  by  using  No.  o  or  larger.  No.  oo  is  a  standard  size 
and  gives  rather  better  service  than  No.  o  in  case  of  con- 
siderable load  being  bunched  at  one  spot.  Assuming  this 
as  the  trolley  wire,  we  may  pass  to  the  track  return. 
The  general  principles  of  this  have  been  very  fully  dis- 
cussed in  Chap.  II.  The  only  thing  needful  here  is  to 
judge  from  the  general  conditions  the  value  to  be  assigned 
to  the  conductivity  of  the  track  as  compared  with  that  of 
the  overhead  system.  In  the  present  case  we  are  prob- 
ably dealing  with  sixty  to  seventy  pound  rails  and  the 
main  line  is  double  tracked.  The  bonding  is,  or  should  be 
made,  good,  and  since  the  total  service  is  not  heavy  the 
track  conductivity  is  of  the  better  class.  It  is  probable 
therefore  that  raising  the  constant  of  equation  3,  Chap. 
I,  to  13  will  fully  take  account  of  the  return.  Were  the 
service  even  lighter  or  the  rails  continuous  we  might  be 
justified  in  assuming  12,  while  with  poor  bonding  and 
heavy  tramc  it  might  be  necessary  to  assume  14. 


80     POWKR   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

Step  o.  Approximate  data  are  now  at  hand  for  laying 
out  the  feeding  system  proper.  We  may  start  with  a 
duplicate  of  Fig.  46,  as  Fig.  48,  showing  now  only  the  actual 
lines  and  H,  the  location  of  the  station.  From  A  to  D  there 
are  two  No.  oo  trolley  wires,  one  for  each  track.  From  C  to 
E  there  is  one  such  trolley  wire.  We  may  now  find  more 
exactly  the  proper  distance  between  feeders.  Beginning 
with  section  i ,  we  find  that  in  regular  traffic  each  trolley 
wire  will  supply  five  cars  at  various  points.  Now  going 
back  to  equation  2,  substituting  our  new  constant  and 
transposing  we  have 

Iv=- 


13  C 

Here  c.  m.  =  133,000,  K  =  25,  and  13  C  =  195.  I,  there- 
fore equals  for  a  single  car  very  nearly  17,000  ft.,  for  two 
cars  8500  ft.  ,  for  three  cars  5666,  for  four  cars  4250,  and  for 
five  cars  3400  ft.  Hence  a  single  feeder  at  the  middle  point  of 
A  B  would  be  sufficient  to  handle  the  average  load  uniformly 
distributed,  very  nicely.  The  same  is  obviously  true  of 
sections  BD  and  CE.  Just  here  appears  the  peculiar 
characteristic  of  railway  systems  —  the  unpleasantly  large 
maximum  loads.  If  the  load  at  the  end  of  A  B  should  be 
300  amperes  as  we  have  supposed,  i.  e.,  150  amperes  to  be 
supplied  by  each  trolley  wire,  the  corresponding  drop  in 
would  be  by  equation  3 


c.  m. 

Which  in  addition  to  the  loss  in  the  feeder  would  produce  a 
total  drop  which  would  be  decidedly  troublesome,  although 
hardly  enough  to  cause  serious  difficulty.  The  cars  would 
run,  but  the  motors  would  heat  badly  and  it  would  be  diffi- 
cult to  make  time.  On  B  D  the  conditions  would  be  better, 
but  with  the  maximum  load  at  E  the  drop  would  be  enough 
to  stall  the  cars  completely  and  they  would  have  to  be  slowly 
worked  away  one  at  a  time. 

As  to  the  effect   of  drop,    with  the  usual   500  voi* 
motors,  a  drop  of   75  to    100  volts  is   decidedly  annoying. 


DIRECT   FEEDING  SYSTEMS.  8 1 

compelling  the  motors  to  slow  down  and  work  inefficiently, 
while  if  the  drop  reaches  125  volts  or  more  the  motors  are 
nearly  inoperative  under  heavy  loads,  although  they  will 
still  work  if  too  great  demands  are  not  put  upon  them.  It 
is  highly  undesirable  to  deal  with  more  than  100  volts  loss 
under  maximum  load  in  a  500  volt  system.  By  overcom- 
pounding  the  generators  these  conditions  can  be  much  re- 
lieved. With  the  maximum  drop  limited  to  twenty  per 
cent,  it  is  clear  that  the  average  drop,  with  the  ordinary 
ratios  between  average  and  maximum  load  would  have  to 
be  limited  to  five  or  at  the  utmost  ten  per  cent. 


FIG.  48. 

If  the  dynamo  be  overcompounded,  as  it  should  be  for 
at  least  the  average  drop,  then  the  maximum  drop  will  gen- 
erally fall  within  safe  limits.  It  is  a  common  practice  to 
overcompound  ten  per  cent,  i.  e. ,  fifty  volts,  so  that  even 
a  total  drop  of  twenty-five  per  cent  will  still  leave  the  sys- 
tem in  fair  operative  condition. 

Coming  back  now  to  Fig.  48,  we  have  found  that  the 
system  is  operative  at  average  load  by  means  of  the  trolley 
wire  alone,  but  should  be  well  re-enforced  by  feeders  to 
meet  the  conditions  of  heavy  load.  Since  we  have  found 
that  feeding  at  the  middle  point  of  A  B  would  give  too- 
much  drop  even  if  the  loss  in  the  feeder  were  as  small  as 
five  per  cent  at  average  load,  the  next  step  is  to  feed  at  two 
points.  These  should  be  so  chosen,  if  the  load  is  uniform 
along  the  section,  as  to  be  one-half  the  length  of  the  see- 


82     POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

tion  apart,  a  and  b  (Fig.  48)  have  this  position.  No  load 
can  therefore  be  more  than  2500  ft.  from  a  feeder.  Now 
consider  the  maximum  load  of  300  amperes  at  A.  Sup- 
pose first  that  the  feeder  H  a  is  to  give  five  per  cent  drop, 
twenty-five  volts  at  average  load.  This  average  (half  the 
total  average  load)  is  seventy-five  amperes.  The  distance 
A  H  is  4500  ft.  ,  the  wire  therefore  must  be  of  area, 


This  is  best  met  by  a  No.  ooo  wire,  which  is  the  nearest 
size  (167,  ooo  c.  m.)  and  will  give  less  than  one  per  cent 
more  drop. 

With  300  amperes  at  A  the  drop  in  the  trolley  wires 
for  2500  ft.  would  be  thirty  six  volts.  The  drop  in  the 
feeder  would  obviously  be  a  little  over  a  hundred  volts, 
making  a  total  quite  too  great,  since  the  overcompound- 
ing,  unless  a  special  generator  be  devoted  to  the  feeder  in 
question  responds  to  the  total  load  on  the  system  and  not 
fully  to  the  load  at  A.  Even  the  gain  from  the  current 
path  along  H  B  a  will  not  relieve  matters  quite  enough. 
Now  we  might  use  a  much  larger  feeder  and  thus  reduce 
the  drop,  but  a  simpler  and  cheaper  way  is  to  cross  tie 
both  feeders  into  the  trolley  lines  at  c.  This,  assuming 
both  feeders  to  be  of  the  same  size,  puts  at  our  disposal  from 
a  to  c  no  less  than  433,000  c.  m.,  with  334,000  c.  m.  for  the 
looo  ft.  between  H  and  C.  The  total  drop  will  then  be 
36  -f-  31  -f-  12  =  79  less  whatever  has  been  gained  from 
the  overcompounding.  This  last  depends  on  the  total 
load  on  the  system  and  is  consequently  indeterminate.  It 
could  hardly  however  be  less  than  half  the  full  overcom- 
pounding, say  twenty-five  volts,  thus  giving  a  net  drop  of 
fifty-  four  volts  at  A. 

This  cross  connecting  process  is  a  very  useful  safe- 
guard against  extreme  terminal  loads,  though  if  the  whole 
line  is  likely  to  have  a  heavy  distributed  load  at  the  same 
time,  it  is  better  to  take  a  different  step  as  will  presently  be 
shown. 


DIRECT   FEEDING   SYSTEMS.  83 

Obviously  a  maximum  load  at  B  will  produce  no 
trouble,  so  that  we  may  pass  to  the  section  B  D.  If  this 
be  fed  in  the  middle  at  d  the  loss  in  the  trolley  wire  at 
average  load  is  very  trifling,  not  more  than  that  due  to  the 
current  for  two  cars  over  each  trolley  wire  at  a  distance  of 
3000  ft. — about  nine  volts.  So  far  then  as  average  loss  is 
concerned  we  could  properly  allot  to  the  feeder  carrying 
ninety  amperes  a  loss  of  forty-one  volts.  If  B  D  and  A  B 
are  connected  at  B  we  can  get  considerable  relief  in  ordi- 
nary states  of  load.  The  worst  possible  load  would  be  300 
amperes  at  B  and  250  at  D.  The  drop  in  B  D  would  then 
be  thirty-six  volts.  Since  with  such  a  compound  load  the 
overcompounding  would  be  up  to  its  full  amount,  we  can 
allow  eighty  to  ninety  volts  loss  between  d  and  the  station. 
If  this  were  all  in  the  feeder  H  d,  it  would  have  to  be  of 
about  288,000  c.  m.  But  on  account  of  the  overcompound- 
ing we  can  get  material  aid  from  the  main  line  up  to  B, 
and  so  will  try  to  make  a  No.  oooo  (2ii,oooc.  m.)  answer 
the  purpose.  If  the  line  via  B  can  be  counted  on  for,  say, 
seventy  amperes,  the  No.  oooo  will  take  the  rest.  With 
370  amperes  the  drop  from  H  to  B  is  about  40  -f-  45  volts 
in  H  c  b  and  B  b  respectively,  less  the  over  compounding, 
while  the  loss  in  B  d  would  be  nominal.  In  fact  a  glance 
at  these  figures  shows  that  a  No.  ooo  will  do  admirably,  for 
our  line  via  B  can  evidently  furnish  considerably  more  than 
seventy  amperes  without  too  much  loss. 

This  settles  the  first  two  sections.  As  to  the  third,  it 
is  evident  at  a  glance  that  it  cannot  be  fed  in  the  middle 
point  since  A  B  with  two  trolley  wires  could  not  be  so  fed, 
while  C  K  has  only  one.  Therefore  a  feeder  should  be  run 
by  the  shortest  route  from  the  station  to  C  H  and  then 
along  the  line  to  K,  for  300  amperes  is  too  much  to  carry 
over  a  No.  oo  trolley  wire,  and  that  load  must  be  dealt  with 
at  K.  Let  H  e  be  this  feeder,  8000  ft.  long,  4000  ft.  being 
along  the  line.  Now  if  we  could  depend  on  stiff  overcom- 
pounding to  help  us  out  at  E,  these  feeders  could  be  quite 
moderate  in  size.  As  it  is  however  the  chances  are  that 
the  load  on  other  parts  of  the  system  would  be  rather  small 


84    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS,. 

when  the  maximum  load  is  to  be  met  at  E.  Therefore  it 
is  not  safe  to  count  on  more  than  twenty  or  twenty-five 
volts  help  from  this  source.  Bearing  this  in  mind  the  first 
thought  would  be  to  try  the  No.  ooo  that  served  for  a  sim- 
ilar load  at  A.  From  F  to  K  we  have  a  No.  ooo  plus  the 
trolley  wire,  i.e. ,  300,000  c.  m.  The  drop  over  this  line  would 
then  be  fifty- two  volts.  It  is  clear  from  this  that  to  come 
within  decent  limits  there  must  be  extra  feeder  capacity 
from  H  to  F.  A  second  No.  ooo  here  would  give  a  drop 
of  forty-six  volts  in  all  from  H  to  F  or  a  total  of  ninety- 
eight  to  K.  This  is  rather  large,  but  considering  the  fact 
that  this  extreme  load  at  K  is  only  occasional  and  at  known 
times  it  is  not  worth  while  installing  still  more  copper. 
Instead,  it  is  a  very  simple  matter  to  raise  the  voltage  at 
the  station  twenty-five  volts  or  so  in  preparation  for  the 
extra  load.  The  feeder  should  be  tied  into  the  trolley  at 
frequent  intervals  near  K  and  once  at  F. 

Step  7.  Now  as  regards  the  line  from  F  to  C,  we  reach 
the  final  step  of  reinforcing  for  the  grade  F  G.  The  simplest 
wray  of  doing  it  is  to  extend  the  feeder  to^-,  connecting  it 
to  the  trolley  wire  at  several  points.  For  a  load  of  even 
300  amperes  at  G  the  drop  would  be  only  46-1-26=72  volts, 
less  the  overcompounding.  On  the  stretch  from  G  to  C 
help  is  received  from  C  so  that  there  is  little  to  be  feared. 

We  have  now  completed  the  feeding  system  and  may 
now  pause  to  take  account  of  stock.  It  aggregates  25,000 
ft.  of  No.  ooo  wire  weighing,  in  "weatherproof"  grade 
about  15,000  Ibs.  and  costing  about  $2250.  It  meets  the 
condition  of  an  average  total  loss  of  less  than  ten  per  cent 
in  the  system  at  average  load  and  gives  not  less  than  425 
volts  at  the  motors  under  the  worst  conditions  of  load. 

It  should  be  noted  that  the  feeders  are  practically 
determined  by  the  requirements  of  maximum  load.  As  a 
general  rule,  if  one  takes  care  of  the  maximum  loads  the 
average  loads  will  take  care  of  themselves. 

To  facilitate  the  calculation  of  feed  wire  Plate  IV 
shows  the  wire  to  be  used  in  transmitting  100  amperes, 
various  distances  up  to  25,000  ft.  at  50  volts  loss,  and  for 


DIRECT   FEEDING    SYSTEMS. 


TOO 


COO 


COO 


2Nc 


OOIK)_ 


S400 


No.  0000 


200 


No.  000_ 


100 


PLATE  IV 
AREA    AND    WEIGHT    OF    COPPER 

required  for  transmitting  100  amperes  for  dis- 
tances of  25000f  eet  and  less,  at  50  volts  loss,  with 
various  constants  for  track  return. 


10  15 

Distance  in  units  of  1000  feet. 


2100 


1950 


1800 


1500 


1200 


1050 


900 


750 


m 


450 


300 


150 


20  25 

Street  Railway  Journal. 


80     POWER   DISTRIBUTION  FOR   ELECTRIC   RAILROADS. 

various  values  of  the  constant  K  which  allows  for  the  con- 
ductivity of  the  track.  The  distances  herein  are  lengths 
of  feeder.  K=i2  is  to  be  used  for  continuous  rails  or  ihe 
most  perfect  bonding,  coupled  with  moderate  service. 
K=  1 3  applies  to  roads  with  very  fine  track  and  heavy  serv- 
ice or  to  roads  with  good  track  and  moderate  service, 
while  K=  1 4  should  be  used  for  roads  having  only  ordinary 
track  and  heavy  -service  or  poor  track  and  ordinary  traffic. 
K==i4  or  15  may  be  needed  when  the  track  return  is  un- 
usually poor,  while  K=n  is  introduced  for  comparison. 

It  should  be  noted  that  the  amount  of  feed  wire  needed 
for  the  case  in  hand  is  very  different  from  that  indicated  in 
the  preliminary  discussion.  This  is  evidently  due  to 
the  face  that  the  actual  wire  is  adjusted  with  reference  to 
maximum  rather  than  average  drop.  It  is  safe  in  looking 
into  the  question  of  distribution,  therefore,  to  figure  the 
approximate  feeder  copper  for  an  assumed  maximum  load 
varying  from  twice  the  assumed  average  in  large  and  level 
roads  to  three  or  even  four  times  the  average  in  small  roads 
with  heavy  grades, 

As  to  the  actual  amount  of  drop  to  allow  circumstances 
vary  widely.  In  most  cases  the  conditions  of  economy  are 
theoretically  met  by  losing  five  to  ten  per  cent  of  the  total 
energy  in  the  distribution.  This  means  that  the  average 
drop  over  the  whole  system,  figured  on  the  average  current 
during  the  hours  of  operation  should  be  from  five  to  ten 
per  cent.  As  a  matter  of  fact  the  average  loss  is  very  often 
determined,  just  as  in  the  case  before  us,  by  the  condition 
that  the  maximum  net  drop  shall  not  exceed  a  certain  fixed 
amount.  This  condition  must  always  be  satisfied  and  it 
seldom  leads  to  an  excessive  average  drop.  In  the  case 
before  us  the  average  loss  on  section  i  is  about  four  per 
cent,  on  section  2  about  six  per  cent,  on  section  3  about 
three  per  cent.  The  average  energy  loss,  therefore,  is  a 
trifle  over  4^  per  cent. 

Including  42,000  ft.  of  trolley  wire,  weighing  about 
17,000  Ibs,  and  costing  about  $2380,  the  total  cost  of  the 
copper  to  give  the  above  loss  would  be,  approximately, 


DIRECT   FEEDING  SYSTEMS.  87 

$4630.  This  cost  would  have  to  be  doubled  to  save  2% 
per  cent  of  the  total  energy.  The  annual  charge  for  this, 
counting  interest  and  depreciation  at  ten  per  cent,  would  be 
$463,  nearly  $206  for  each  per  cent  saved.  Now  the  amount 
of  power,  based  on  the  average  amperes,  is  about  2700  k.w. 
hours  per  day  of  eighteen  hours;  the  cost  of  this  per  year 
at  two  cents  per  kilowatt  hour  would  be  $19,710,  of  which 
one  per  cent  is  $197.10,  showing  that  it. probably  will  not 
pay  to  increase  the  investment  in  copper. 

The  art  of  feeder  design  is  one  that  calls  for  great 
finesse  and.  skilled  judgment  in  assigning  the  proper  values 
to  the  somewhat  uncertain  maximum  loads.  It  cannot  be 
reduced  to  formulae  that  will  be  of  use  in  anything  save 
special  and  unusual  circumstances.  The  author  has  in  this 
chapter,  therefore,  merely  attempted  to  give  the  general 
principles  to  be  followed  and  some  idea  of  the  mental  pro- 
cesses by  which  the  final  approximation  is  reached.  In 
another  chapter  the  special  case  of  long  interurban  lines 
will  ^e  considered. 


CHAPTER  IV. 

SPECIAL   METHODS   OP   DISTRIBUTION. 
* 

It  is  quite  obvious  that  the  use  of  about  500  volts  as 
working  potential  for  railway  purposes  entails  a  very 
serious  cost  of  copper  on  lines  of  any  considerable  length, 
for  in  general  the  cost  of  copper  for  a  given  proportion  of 
energy  wasted  varies  inversely  with  the  square  of  the 
voltage. 

For  instance,  to  deliver  500  amperes  at  ten  miles  dis- 
tance would  require,  even  with  a  gross  drop  of  150  volts, 
about  2,000,000  c.  m.  of  copper  area  weighing  about  three 
tons  per  1000  ft.;  in  all  over  150  tons,  costing  not  far  from 
$45,000,  about  $225  per  kilowatt  of  energy  delivered. 

It  is,  of  course,  highly  desirable  to  find  means  for 
reducing  this  excessive  cost  and  all  sorts  of  expedients 
have  been  tried  to  that  end.  The  gross  loss  above  assumed 
is  about  as  great  as  can  be  permitted,  since  on  a  line  with 
distributed  load  more  loss  and  greater  overcompounding  is 
likely  to  interfere  with  the  proper  performance  of  the 
motors  and  the  regularity  of  the  schedule.  Very  heavy 
overcompounding  increases  the  cost  of  the  generators  and 
leads  to  extremes  of  voltage.  In  dealing  with  such  a  case 
as  that  just  cited  the  most  frequently  advantageous 
method  would  be  to  fall  back  on  some  of  the  regular 
methods  of  power  transmission  which  will  be  described 
later,  but  under  some  circumstances  the  substation  involved 
in  these  methods  is  undesirable,  and  one  must  either  stand 
the  heavy  expenditure  for  copper  or  adopt  some  special 
means  for  reducing  it. 

There  are  several  of  these  that  are  in  fairly  successful 
use.  Of  those  which  require  no  special  devices  in  connec- 
tion with  the  motors  the  most  generally  applicable  is  the 


SPECIAL,   METHODS   OF   DISTRIBUTION  89 

so  called  "  booster"  system  which  is  essentially  a  method 
of  raising  the  voltage  on  the  feeders  when  the  conditions  of 
load  demand.  Fig.  49  gives  a  general  idea  of  its  character. 
A  B  is  the  line  which  it  is  desired  to  feed,  C  the  main  gene- 
rator connected  to  the  track  and  ground  return  at  E,  and 
D  the  boosting  generator  for  raising  the  voltage  on  A  B. 

This  booster  is  a  relatively  small  dynamo  connected  in 
series  with  the  main  one.  Its  voltage  is  proportioned  to 
the  extra  voltage  desired  on  A  B,  and  its  capacity  in  cur- 
rent is  equal  to  the  demands  of  A  B.  Its  function  is  to 
supply  the  energy  which  must  be  lost  in  the  line  in  order 
to  reduce  the  cross  section  of  the  line  copper  while  preserv- 
ing the  proper  voltage  and  output  at  B.  It  is  driven  by 
any  convenient  motive  power,  generally  in  practice  by  an 


FIG.  49. 

electric  motor.  In  Fig.  49  the  booster  voltage  is  taken  at 
200,  while  we  will  assume  that  500  amperes  are  to  be 
delivered  as  in  the  case  just  discussed.  The  capacity  of 
the  booster  would  then  have  to  be  100  k.  w.,  while  that  of 
the  main  generator  might  be  anything  that  local  conditions 
on  the  system  should  demand.  The  effect  of  the  boosting 
system  is  quite  obvious.  The  initial  combined  voltage 
would  be  750,  of  which  300  volts  might  be  lost  in  the  line. 
The  result  would  then  be  to  reduce  the  copper  needed  in 
the  line  to  one-half  of  its  former  amount.  The  cost  of  the 
booster  and  its  equipment  including  motive  power  would 
be  $5000  to  $4000,  so  that  there  would  be  a  net  gain  of 
nearly  $20,000  in  first  cost  of  equipment.  Reckoning,  as 
in  our  previous  example,  interest  and  depreciation  on  this 
at  ten  per  cent,  there  is  a  gross  saving  of  about  $2000  per 
year  to  offset  the  cost  of  the  extra  power  lost  in  transmis- 


90     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

sion.  This  extra  loss  amounts  to  seventy-five  kilowatts.  At 
two  cents  per  kilowatt  hour  the  cost  of  the  lost  energy  is 
$1.50  per  hour  of  continuous  service.  If  the  booster  were 
a  part  of  a  system  demanding  the  output  rather  steadily  for 
the  full  day's  run,  say  eighteen  hours,  the  cost  of  energy 
lost  would  be  no  less  than  $9855  per  year.  This  simply 
means  that  it  seldom  or  never  pays  to  lose  so  great  a  pro- 
portion of  energy  in  transmission.  It  is  evident,  however, 
that  it  will  pay  to  use  the  booster  up  to  about  three  hours 
per  day  of  service  at  full  load.  It  is,  therefore,  well  suited 
for  helping  to  tide  over  the  times  of  unusually  heavy 
traffic.  Plate  V  shows  a  typical  motor  boosting  set. 

We  have  already  seen  that  these  extreme  loads  really 
determine  the  copper  necessary  for  feeders,  so  that  the 
booster  system,  if  used  judiciously,  may  save  a  large 
investment  in  copper  at  the  cost  of  an  amount  of  wasted 
energy  that  is  well  within  the  bounds  of  economy.  The 
system  is  therefore  much  better  suited  to  the  operation  of 
long  feeders  than  to  the  more  general  use  of  a  station. 
Such  indeed  was  its  original  use  in  incandescent  electric 
lighting  at  low  voltage.  It  has  proved  for  this  purpose 
very  useful  indeed,  rendering  it  possible  to  take  up  the 
loss  in  long  feeders  at  times  of  heavy  load,  and  to  operate 
lines  too  long  to  form  a  proper  part  of  the  main  system. 
It  thus  has  a  very  useful  field  in  connection  with  existing 
plants,  but  it  is  distinctly  an  adjunct,  not  a  proper  general 
method.  Line  losses  which  necessitate  the  continuous 
waste  of  more  energy  than  can  be  compensated  by  the  ordi- 
nary compound  wound  generators  are  seldom  or  never  jus- 
tifiable even  in  a  portion  of  an  extended  system.  If  thus 
partial  they  are  simply  less  bad  than  if  the  whole  plant 
violated  the  conditions  of  economy.  In  its  proper  sphere 
the  booster  accomplishes  the  same  end  as  the  employment 
of  extra  voltage  in  the  generators  in  a  case  such  as  was 
suggested  in  the  last  chapter. 

As  in  every  other  case  oft  heavy  drop  in  the  line  the 
boosting  system  involves  certain  difficulties  in  preserving 
sufficiently  uniform  voltage  along  the  whole  line.  When 


SPECIAL   METHODS   OF   DISTRIBUTION. 


Q2       POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

properly  applied  for  railway  purposes  it  should  become 
the  equivalent  of  an  enormous  overcompouuding  applied, 
not  to  the  whole  system,  but  only  to  such  parts  of  it  as  re- 
quire reinforcement.  Take  the  case  of  a  simple  interurban 
road  (Fig.  50).  Its  office,  let  us  suppose,  is  to- connect 
cities  C  and  D  in  addition  to  handling  a  considerable  local 
traffic  in  D  and  a  larger  one  in  C.  The  power  station, 
at  A,  was  originally  devoted  to  the  local  work  in  C  and  now 
has  to  be  utilized  to  operate  the  whole  system.  The  dis- 
tance from  A  to  B,  the  center  of  distribution  in  D,  is  ten 
miles.  Under  what  circumstances  and  how  may  the 
boosting  system  be  profitably  employed  ?  Let  the  maxi- 


FIG.  50. 

mum  sustained  output  in  D  be  500  amperes,  including 
both  local  traffic  and  interurban  cars.  From  what  has 
already  been  said  it  is  clear  that  if  these  500  amperes  were 
needed  continuously  the  booster  system  would  be  simply  a. 
rat  hole  into  which  the  management  would  pour  about 
$8000  per  year.  On  the  other  hand  if  the  500  amperes  is 
a  maximum  load  reached  normally  only  a  couple  of  hours 
a  day,  boosting  could  be  profitably  employed.  No  system 
is  better  fitted  for  furnishing  additional  power  over  moder- 
ate distances  during  brief  periods  of  excessive  load.  Just 
how  long: boosting  could  be  used  to  advantage  would  de- 
pend on  the  character  of  the  variations  in  the  load.  The 
general  rule  regarding  the  economics  of  the  matter  is  that 
a  drop  in  the  line  great  enough  to  necessitate  boosting  at 
average  load  is  never  justified,  while  if  at  an  economical 
average  drop  the  drop  at  maximum  load  is  too  great  tc  be 


SPECIAL    METHODS   OF   DISTRIBUTION.  93 

conveniently  overcome  by  ordinary  compounding,  boosting 
is  eminently  useful. 

If  the  line  A  B  (Fig.  50),  when  designed  for  a  certain 
drop  at  average  load,  say,  five  per  cent,  gives  no  more 
than  fifteen  per  cent  or  so  at  maximum  load  ordinary  over- 
compounding  will  answer  admirably.  If,  however,  the 
maximum  load  rises  to  five  or  six  times  the  average 
for  which  the  line  was  designed  boosting  is  by  far  the 
simplest  way  out  of  the  difficulty. 

Suppose  now  A  B  to  be  fifteen  or  twenty  miles  long 
and  to  have  a  heavy -and  fast  interurban  traffic.  Could  it 
be  worked  to  advantage  by  supplying  current  directly  to 
that  part  of  the  line  comfortably  near  the  power  station 
and  feeding  the  rest  of  the  line  by  boosting  in  sections 
using  boosters  of  different  voltage  if  necessary  ?  At  first 
thought  one  might  be  tempted  to  say  ' '  Yes' ' ,  for  in  such 
case  each  section  would  be  in  full  action  for  but  a  short 
part  of  the  day.  On  the  other  hand  it  should  be  noted 
that  all  the  energy  supplied  to  the  distant  sections,  be  it 
little  or  much,  is  supplied  under  very  wasteful  conditions, 
and  while  such  an  arrangement  would  allow  a  very  long 
line  to  be  served  there  is  generally  no  excuse  in  the  pres- 
ent state  of  the  art  for  a  device  so  clumsy  and  wasteful. 

It  must  not  be  understood  from  this  that  there  are  no 
cases  in  which  direct  transmission  at  more  than  usual  line 
loss  is  to  be  preferred  to  indirect  transmission  with  recon- 
version. Such  certainly  exist,  but  since  at  the  present 
time  it  is  possible  to  transmit  power  at  high  voltage  and 
reconvert  to  direct  current  with  a  loss  not  exceeding  fif- 
teen to  twenty  per  cent,  the  field  for  direct  transmission  at 
much  greater  loss  is  very  limited. 

Boosting  is  preferable  to  heavy  overcompounding 
when  unusually  long  feeders  are  exposed  to  great  changes 
of  load,  for  the  reasons  already  suggested,  and  it  must  not 
be  forgotten  that  when  the  only  loss  is  that  in  the  line 
which  varies  inversely  as  the  load,  the  all-day  efficiency 
of  the  system  may  be  fairly  high.  This  matter  will 
be  taken  up  again  in  connection  with  the  application  of  the 


94       POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

methods  of  alternating  current  transmission  to  cases  like 
that  of  Fig.  50. 

Better  than  any  method  of  increasing  the  loss  in  the 
line  are  various  methods  of  increasing  the  working  voltage. 
These  effect  the  same  or  greater  economy  in  copper  with 
less  loss  of  energy  and  are  in  very  many  cases  preferable 
to  any  boosting  scheme.  Some  of  them  are  simply  ap- 
plicable without  any  changes  in  the  arrangement  of  the 
motors,  while  others  require  special  motors  or  special 
arrangements  of  them. 

The  application  of  the  Edison  three- wire  system  is  the 
most  generally  known  of  these.  Its  principles  are  by  this 
time  very  familiar  to  the  public,  consisting  virtually  of 


Street  Ry.  Journal 

FIG.  51. 

employing  two  working  devices  in  series  as  regards  the 
voltage  of  transmission,  while  each  separate  device,  con- 
nected between  one  of  the  transmission  wires  and  the 
neutral  wire,  receives  only  the  voltage  for  which  it  is  de- 
signed. The  application  of  this  device  to  railway  work  is 
well  shown  in  Fig.  51.  The  outside  terminals  of  the  two 
generators  are  connected  to  two  trolley  wires  while  the 
neutral  is  connected  to  the  track  system.  Hence  each 
motor  works  on  about  500  volts,  while  the  transmission  of 
the  total  energy  is  at  1000  volts. 

In  this  case  the  neutral  wire  is  the  track,  which  ordi- 
narily, as  we  have  seen,  has  a  rather  good  conductivity  so 
that  the  saving  in  copper  is  very  material.  If  the  loads  on 
the  two  sides  of  the  system  were  perfectly  balanced  so  that 
there  would  be  no  steady  flow  through  the  neutral  wire, 


SPECIAL   METHODS   OF   DISTRIBUTION.  95 

the  feeder  copper  could  obviously  be  reckoned  as  if  we 
were  dealing  with  a  1000  volt  transmission  through  a  com- 
plete metallic  circuit.  For  the  same  percentage  loss  of 
energy  the  copper  required  will  be  apparently  less  than  half 
that  needed  on  the  500  volt  system.  The  case  is  widely 

-f. C  =  1000 


FIG.  52. 

different  from  that  of  a  lighting  circuit  since  in  the  latter 
we  are  comparing  two  complete  metallic  circuits,  one  of 
double  the  voltage  of  the  other,  while  in  the  former  we  are 
comparing  a  very  good  '  'grounded'  '  circuit  with  a  return  cir- 
cuit of  double  the  voltage.  In  other  words  the  track,  which 
as  a  return  conductor  serves  a  very  important  purpose,  as  a 
'  '  neutral  "  is  in  use  only  so  far  as  the  system  is  unbalanced 
and  to  serve  the  purpose  of  a  local  conductor  between 
cars.  To  illustrate  by  a  concrete  case,  suppose  a  load  of 


=  500 


Sr                      ^                                          C-=U7Vfldt 

L=250J£.TF. 

0                                                                                                                           L^K.W. 

FIG.  53- 

500  k.  w  is  to  be  operated  at  a  distance  of  5000  ft.  from  the 
station.  For  simplicity  we  will  suppose  it  to  consist  of  a 
mass  of  cars  bunched  on  a  double  track.  With  the  ordi- 
nary system  we  have  the  state  of  things  shown  in  Fig.  52. 

Using  the  constant  13  in  our  stock  formula,  the 
total  area  of  copper  comes  out  1,300,000  c.  m.  As  a  three- 
wire  system  in  complete  balance  we  have  the  conditions  set 
forth  in  Fig.  53. 

Here  we  employ  the  ordinary  formula  for  metallic 
circuits  and,  of  course,  the  constant  n.  The  copper  con- 
sequently amounts  to  550,000  c.  m.  in  area  and  since  both 


96       POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

leads  must  have  this  area  the  total  weight  of  copper  neces- 
sary is  as  ii  to  13  compared  with  the  500  volt  arrange- 
ment. The  enormous  conductivity  of  the  neutral,  however, 
renders  the  matter  of  balance  of  comparatively  little  im- 
portance in  this  case. 

The  somewhat  anomalous  character  of  this  result  has 
its  origin  in  the  fact  that  the  track,  which  is  or  ought  to  be 
a  first  class  conductor,  is  fully  utilized  in  Fig.  52,  while  in 
Fig.  53  it  can  only  come  to  the  rescue  when  the  system  is 
unbalanced. 

This  arrangement  of  the  three- wire  system  is  capable  of 
accomplishing  a  notable  saving  of  copper  only  when  the  track 
is  so  poor  as  a  conductor  that  14  or  15  has  to  be  used  as  the 
constant  in  the  computation  concerning  Fig.  52.  There  is, 
however,  another  distinct  species  of  three- wire  system  which 
is  capable  of  giving  greater  economy  for  certain  work. 

Suppose  we  make  connections  as  in  Fig.  54.  Here 
the  outside  wires  are  connected  one  to  an  overhead  line, 
the  other  to  the  track,  while  the  second  overhead  line 
serves  as  the  neutral.  The  motors  may  then  be  connected 
either  on  500  or  1000  volts,  an  arrangement  which  would 
be  valuable  for  interurban  work  with  special  motors. 
This  arrangement  is  not,  however,  suited  for  general  use, 
and  should  be  regarded  as  a  mixed  system,  which,  how- 
ever, is  excellently  fitted  for  certain  otherwise  difficult 
work.  It  is  closely  related  to  a  booster  system,  the 
booster  not  being  used  in  the  ordinary  way  to  compensate 
for  line  loss,  but  to  give  a  higher  working  voltage  on 
lines  where  it  is  needed.  The  two  dynamos  need  not  be 
of  the  same  voltage. 

The  regular  three- wire  system  of  Fig.  53  is  capable  of 
saving  from  fifteen  to  forty  per  cent  "in  copper  according 
to  the  character  of  the  track  return.  If  well  balanced  it, 
of  course,  tends  greatly  to  diminish  the  electrolytic  action 
on  buried  conductors  and  hence  is  desirable  per  se.  The 
saving  in  copper,  while  by  no  means  as  great  as  in  the 
three-wire  system  for  lighting  may  be  sufficient  to  pay  for 
the  difficulty  of  installation  and  the  expedient  has  been 


SPECIAL   METHODS  OF  DISTRIBUTION.  97 

adopted  by  several  roads.  Balancing  is  accomplished  by 
various  means.  The  simplest  is  shown  in  Fig.  55.  Here 
\ve  have  a  single  track  road  with  two  lines,  A  B  and  C  D. 
The  tracks  are  connected  to  the  neutral  lead  while  the  -f- 
and  —  feeders  run  to  the  separate  branches  as  shown. 
This  balancing  is  not  very  close  since  it  is  no  easy  matter 


Track 

FIG,  54. 

so  to  divide  a  branched  road  that  the  loads  on  the  two 
parts  shall  be  equal.  Another  arrangement  less  simple, 
but  giving  more  uniform  balance,  is  shown  in  Fig.  56. 
Here  the  whole  track  is  divided  into  sections  alternately  -j- 
and  —  .  On  double  roads  either  one  track  is  supplied  from 
the  +  feeder  and  the  other  from  the  —  ,  or  each  track  is 
subdivided  as  in  Fig.  56,  the  latter  being  the  preferable 
method  as  it  preserves  the  loads  on  the  two  sides  more 
uniformly. 


A  zonal  system  might  be  used  in  large  systems,  all 
track  within  one  zone  being  supplied  from  the  +  side,  all 
in  the  next  zone  from  the  —  side  and  so  on.  In  general 
however  the  plan  of  Fig.  56  carried  out  on  all  the  lines  as 
systematically  as  the  location  of  the  track  allows  is  the  best 
method.  The  sections  may  properly  vary  from  a  few  hun- 
dred to  several  thousand  feet  in  length  according  to  the 
nature  of  the  car  service  arid  local  conditions.  Very  many 
sections  should  be  avoided  as  the  break  pieces  in  the  trolley 
wire  are  somewhat  annoying. 


98      POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

The  three- wire  system  was  tried  as  far  back  as  1889 
in  Milwaukee  and  has  been  employed  with  rather  moderate 
success  in  Portland,  Ore.;  Bangor,  Me.;  St.  L,ouis  and 
elsewhere. 

Unhappily  while  balancing  under  ordinary  conditions 
is  not  overtroublesome  that  wandering  of  the  load  which 
is  so  grave  a  factor  in  electric  railway  work,  has  been 
found  to  produce  serious  unbalancing  at  times  so  that  the 
three- wire  system  is  at  present  in  rather  ill  repute. 

On  the  whole  the  three- wire  distribution  may  be  use- 
ful, but  is  not  easily  managed  except  in  specially  favorable 
cases.  The  saving  in  copper  entails  no  sacrifice  of  effi- 
ciency and  but  little  added  expense  if  the  station  is  large 
enough  to  make  the  use  of  two  dynamos  instead  of  one, 
of  little  moment.  Above  a  certain  size,  the  price  of  dyna- 


FIG.  56. 

mos  increases  almost  directly  as  their  out-put,  so  that  a 
pair  of  machines  for  three-wire  work  would  then  be  little  if 
any  more  expensive  than  one  large  one  of  equal  capacity. 

A  curiously  modified  three-wire  system  has  been  sug- 
gested for  heavy  interurban  work,  although  it  has  not  yet 
come  into  use.  This  is  connected  like  Fig.  53,  except  that 
both  +  and  —  sides  of  the  system  are  connected  to  trolley 
wires  over  the  same  track.  Two  trolleys  are  used  on  each 
car  so  that  the  car  is  a  unit  balanced  in  itself,  the  two 
motors  taking  current  from  the  +  and  —  wires  respectively. 
Fig.  57  shows  this  arrangement  in  diagram. 

Here  A  and  B  are  the  generators  connected  respect- 
ively to  +  and  —  trolley  wires,  and  the  track  forms  the 
neutral.  The  motors  C  and  D  upon  the  same  car  take  cur- 
rent from  the  trolleys  E  and  F  and  are  grounded  upon  the 
track  neutral  in  the  ordinary  way.  The  neutral  only 
comes  into  service  in  the  case  of  need  for  cutting  out  one 


SPECIAL   METHODS   OF  DISTRIBUTION.  99 

motor,  or  when  one  motor  slips  or  develops  faults  that 
might  cause  trouble  were  the  motors  simply  in  series. 
The  track  need  not  be  heavily  bonded  with  this  construc- 
tion since  it  has  to  carry  only  occasional  and  moderate  cur- 
rents. The  saving  in  copper  is  the  same  as  that  already 
indicated  for  the  regular  three-wire  system,  with  the  ad- 
ditional advantage  that  the  track  connections  are  easily 
made  and  do  not  require  so  great  and  constant  care  as  is 
the  case  when  a  full  track  return  is  used. 

The  employment  of  two  trolleys  would  be  considered 
a  first  class  nuisance  by  most  electric  railway  managers, 
but  for  heavy  work  when  large  currents,  say  a  couple  of 


•i. 


t 


FIG.  57. 

hundred  amperes,  are  to  be  dealt  with,  there  is  something 
to  be  said  in  favor  of  trolley  contacts  in  duplicate.  These 
granted,  they  can  be  made  on  two  trolley  wires  without 
much  extra  trouble. 

This  self  contained  three-wire  system  appears  fairly 
adapted  for  heavy  inter  urban  service,  particularly  in  con- 
junction with  local  service  at  the  termini.  As  the  motors 
are  comparatively  independent  of  ground  connections  the 
track  could  be  more  easily  kept  in  operative  condition 
through  the  winter.  The  system  lends  itself  very  readily 
to  cases  like  Fig.  50,  in  which  the  interurban  cars  could 
well  be  connected  in  the  manner  described  and  the  local 
cars  in  the  ordinary  fashion  of  three-wire  roads. 

None  of  the  methods  so  far  described  are  able  to  effect 
a  really  satisfactory  saving  in  copper,  without  involving 
special  arrangements  that  have  proved  somewhat  serious  in 
practice.  Boosters,  using  the  word  in  its  ordinary  sense, 
waste  energy  in  a  very  objectionable  manner,  increasing 


IOO     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

the  drop  without  raising  the  working  voltage  at  the  motors. 
The  ordinary  three-wire  system  involves  complication  in 
the  general  wiring  and  does  not  secure  nearly  as  much 
economy  in  copper  as  would  be  desirable;  the  system  of 
Fig.  54,  while  giving  considerable  economy  on  the  high 
voltage  side  requires  a  special  arrangement  of  motors;  and 
finally  the  self  contained  three-wire  system,  with  several 
excellent  properties,  demands  two  trolleys. 

What  is  really  wanted  for  long  interurban  lines  is  some 
way  of  raising  the  working  pressure  on  the  line,  without 
wasting  much  energy  or  introducing  troublesome  complica- 
tions. It  must  be  clearly  understood  that  as  a  matter  of 
economy  the  higher  the  voltage  the  better,  providing  that 
voltage  can  be  utilized.  If  there  were  no  practical  objec- 
tions to  employing  a  2000  volt  trolley  system  it  would  cer- 
tainly be  used  in  preference  to  juggling  with  a  nominal  500 
volt  system  in  the  rather  vain  attempt  to  cheat  Ohm's  law 
out  of  its  due  tribute  of  copper.  By  far  the  simplest  way 
of  dealing  with  the  long  distance  lines  now  frequently 
found  is  to  face  the  matter  squarely  and  see  what  can  be 
done  in  the  line  of  a  higher  working  pressure  on  the  line 
and  at  the  motors.  It  is  all  very  well  to  work  out  the  most 
economical  methods  for  supplying  500  volt  motors  at  long 
distances,  but  all  such  are  wasteful  in  the  extreme  com- 
pared with  systems  working,  so  far  as  transmission  is  con- 
cerned, with  looo  volts  or  more.  Boosters  and  the  three- 
wire  system  merely  make  the  best  of  a  very  bad  matter. 

In  the  early  days  of  electric  railways  even  500  volts 
was  considered  rather  too  high  a  voltage  for  motors  and 
dynamos  adapted  to  the  severe  strains  of  railway  work. 
A  few  years  of  experience  have  shown  that  with  proper 
care  500  volt  apparatus  is  entirely  reliable  and  in  very 
many  railway  systems  the  working  pressure  is,  save  at 
times  of  very  heavy  load,  nearer  600  volts  than  500.  The 
vSaving  in  copper  introduced  by  even  a  moderate  increase  in 
working  pressure  is  very  considerable,  since,  other  things 
being  equal,  the  weight  of  copper  required  is  inversely  as 
the  square  of  the  voltage.  The  following  table  gives  the 


SPECIAL,   METHODS   OF   DISTRIBUTION.  IOI 

relative  amounts  of  copper  for  a  few  moderate  voltages,  that 
necessary  at  500  volts  initial  pressure  being  taken  as  ICJQ. 
The  same  percentage  of  drop  is  assumed  in  each  case. 

Volts.  Copper. 

500  lop.o 

550  82.6 

600  69.4 

650  59-i 

700  51.0 

750  44.4 

800  39.1 

850  34.6 

900  30.8 

950  27.7 

looo  25.0 

The  actual  results  are  slightly  better,  even,  than  these 
figures  indicate,  since  the  track  return  gets  relatively  better 
and  better  as  the  voltage  rises  and  the  current  diminishes. 
To  show  this  we  may  profitably  take  a  concrete  example. 
Fifty  kilowatts  is  to  be  transmitted  25,000  ft.  for  railway 
purposes.  The  track  is  of  sixty  pound  rail,  and  we  will 
for  simplicity  assume  that  the  bonding  doubles  its  resistance. 
The  conductivity  of  the  track  return  is  then  that  of  one 
continuous  line  of  sixty  pound  rail  which  equals  1,000,000 
c.  m.  of  copper.  At  500  volts  initial  pressure  and  twenty 
per  cent  gross  loss,  the  drop  through  the  track  circuit 
would  be  27.5  volts,  leaving  72.5  volts  drop  for  the  over- 
head line.  This  requires  about  379,000  c.  m.  At  1000 
volts  initial  pressure  the  drop  in  the  track  circuit  would  be 
but  13.75,  leaving  186.25  f°r  the  overhead  system,  which 
corresponds  to  nearly  74,000  c.  m.,  a  trifle  less  than  twenty 
per  cent  of  the  copper  needed  for  500  volts,  instead  of 
twenty-five  per  cent  as  called  for  by  the  table. 

Obviously  this  difference  depends  on  the  fact  that  one 
side  of  the  circuit  is  a  fixed  quantity  of  equal  conductivity 
for  all  voltages  and  currents,  while  this  conductivity  is  a 
factor  entering  the  computation  of  the  rest  of  the  circuit 
when  different  voltages  are  under  consideration. 

The  economic  value  of  working  at  higher  voltages 
than  customary  is  thus  very  evident ,  even  if  one  may  not 
be  prepared  for  boldly  advancing  to  1000  volts  or  more. 


01'   THE 

UNIVERSITY- 


IO2     POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

So  far  as  apparatus  is  concerned  the  difficulty  of  some- 
what higher  voltage  does  not  appear  to  be  very  serious. 
With  comparatively  little  modification  the  type  of  railway 
motor  now  common  could  be  rendered  suitable  for  pressures 
up  to  750  volts  certainly.  The  principal  changes  would  be 
in  the  armature  winding  and  the  commutator,  which  would 
have  to  be  arranged  with  more  segments  to  bring  the  volt- 
age per  bar  within  safe  limits.  With  the  large  and  power- 
ful motors  likely  to  be  used  on  long  interurban  roads  the 
task  is  by  no  means  formidable,  and  should  not  involve  any 
serious  increase  of  cost.  As  regards  the  generators  the 
case  is  similar.  On  very  large  units  1000  volts  would 
probably  involve  difficulties  of  some  moment,  since  in  de- 
signing machines  for  great  outputs,  1000  k.  w.  and  the 
like,  it  is  somewhat  troublesome  to  keep  the  volts  per  com- 
mutator segment  within  reasonable  limits  even  for  600 
volts.  But  under  ordinary  conditions  a  generator  for  750 
to  1000  volts  is  entirely  feasible,  and  for  very  large  capaci- 
ties the  direct  coupled  units,  consisting  of  one  engine  and 
two  dynamos,  already  largely  used,  are  entirely  available. 
Such  a  combination,  shown  in  Fig.  58,  may  be  very  readily 
operated  with  the  generators  coupled  in  series,  giving  1000 
volts  across  the  mains,  or  if  convenient,  500  volts  on  each 
side  of  a  three- wire  system.  In  some  cases,  where  so  much 
as  1000  volts  is  not  desired,  a  boosting  dynamo  may  be 
used  with  great  advantage  in  connection  with  a  500  volt 
generator. 

At  all  events  the  question  of  supplying  current  at  a 
pressure  considerably  in  excess  of  500  volts  is  very  simply 
answered  in  any  of  the  ways  mentioned. 

One  instinctively  asks,  too,  why  ordinary  railway 
motors  should  not  be  operated  regularly  in  series  for  work 
on  long  lines,  as  they  are  very  extensively  employed  now 
with  series-parallel  controllers.  There  is  no  good  reason 
why  this  should  not  be  done,  save  the  danger  of  excessive 
and  destructive  voltage  in  case  of  accident  to  one  motor. 

Of  course,  in  ordinary  series-parallel  working,  no  acci- 
dent could  throw  on  a  single  motor  more  than  the  500  volts 


SPECIAL   METHODS   OF   DISTRIBUTION. 


103 


or  so  for  which  it  is  designed,  while  if  both  motors  were 
in  series, on  a  1000  volt  circuit,  a  short  circuit  in  one  of 
them,  would  probably  cripple  its  mate.  Even  slipping  of 
one  might  overload  the  other  and  imperil  both.  On  the 
other  hand,  serious  relative  slipping,  throwing  the  load  on 


FIG.  58. 

one  motor  when  operating  in  series,  is  not  common  on  the 
dirty  city  streets  where  the  series  connection  is  most  used, 
and  would  be  still  less  likely  to  occur  on  the  comparatively 
clean  and  unobstructed  tracks  of  a  long  line.  When  one 
set  of  wheels  slips  the  other  soon  follows  suit,  from  the 
same  cause,  and  there  is  usually  a  strong  mechanical  ten- 
dency to  equalize  slipping.  Even  admitting  the  difficulty, 
there  would  certainly  be  no  serious  trouble  of  this  sort  if 


104    POWER   DISTRIBUTION   FOR'  ELECTRIC  RAILROADS. 

both  motors  were  constructed  with  a  larger  factor  of 
safety  for  temporarily  enduring  high  voltage  than  is  now 
the  custom. 

There  is  no  momentous  difficulty  in  the  way  of  build- 
ing a  motor  to  work  regularly  at  700  to  750  volts,  and  still 
less  in  producing  one  to  stand  that  pressure  for  temporary- 
running.  And  motors  which  will  stand  750  volts  at  a 
pinch  can  safely  be  operated  two  in  series  on  1000  volts 
with  a  quite  moderate  rheostat  capacity. 

Of  course,  the  question  of  safety  enters  into  any  and 
all  plans  for  operating  at  increased  voltages. 

Of  500  volt  continuous  currents  it  can  safely  be  said 
that  they  have  very  rarely  caused  the  death  of  a  human 
being  in  normal  health.  Of  shocks  to  employes  there  are 
thousands  yearly  and  the  author  has  yet  to  hear  of  a  fatal 
one.  The  deaths  from  this  cause  heralded  in  the  news- 
papers generally  turn  out  to  have  been  due  to  other  causes. 
One  loudly  proclaimed  from  Maine  to  California,  was  due 
to  a  gasoline  explosion  in  a  car  house,  another  to  a  collision 
with  an  electric  railway  pole,  and  so  on. 

Whether  this  immunity  may  be  extended  to  double  the 
usual  voltage  is  decidedly  open  to  question.  Currents  of 
7  50  to  1000  volts  cannot  on  the  other  hand  be  classed  as 
extremely  dangerous  although  quite  capable  of  producing 
fatal  results  under  favorable  conditions.  In  any  case  there 
is  no  good  reason  why  they  should  not  be  freely  employed 
with  good  construction  and  proper  inspection.  In  inter- 
urban  work  the  tendency  is  for  the  road  to  own  its  right 
of  way,  and  in  such  case  any  desired  voltage  ought  to  be 
permitted,  provided  it  be  installed  with  due  precautions. 

To  summarize  the  matter,  there  is  no  sufficient  reason, 
electrical,  mechanical  or  ethical,  why  roads  of  the  inter- 
urban  class  should  not  be  regularly  operated  at  from  700  to 
looo  volts,  either  with  special  motors  or  with  special  ar- 
rangements for  series  running. 

A  rise  from  500  to  750  volts  would  more  than  cut 
the  cost  of  copper  in  two,  while  retaining  at  least  the  effi- 
ciency reached  at  the  lower  voltage.  At  looo  volts  more 


SPECIAL   METHODS   OF   DISTRIBUTION.  105 

than  three-fourths  of  the  copper  would  be  saved,  with  the 
additional  advantage  of  using  standard  generators  instead 
of  those  of  somewhat  abnormal  voltage. 

It  is  a  fact  to  be  regretted  that  in  spite  of  the  great 
advantage  of  even  moderate  increases  in  voltage  most  of 
the  existing  interurban  roads  have  hastily  gone  ahead  and 
equipped  themselves  with  500  volt  apparatus.  There  is 
generally  some  conservative  adviser  to  say,  "  Well  I  think 
copper  is  a  pretty  good  investment;  let  us  stick  to  the 
well  tried  500  volt  apparatus."  True,  copper  is  a  very 
safe  investment,  so  safe  that  money  once  locked  up  in 
it  never  gets  out  again,  and  500  volt  apparatus  is  "  well 
tried,"  but  so  also  is  no  volt  apparatus,  and  for  a  still 


FIG.  59. 

longer  period.  The  point  of  the  matter  is  that  most  men 
do  not  realize  that  standard  apparatus  can  be  made  to  give 
good  results  in  more  than  one  way. 

A  short  investigation  of  the  interurban  line  shown  in 
Fig.  50  will  show  how  terribly  uneconomical  is  the  method 
of  operating  too  often  employed,  and  how  the  conditions 
can  be  greatly  improved  without  involving  anything  in  the 
least  degree  truly  experimental. 

The  problem  really  involved  in  equipping  roads  of  this 
sort  is  as  follows  :  given  standard  motors  and  generators 
as  the  basis  of  operations,  so  to  utilize  them  as  to  give  the 
greatest  economy  in  construction  and  operation  with  the 
fewest  possible  variations  from  every-day  practice. 

Fig.  59  shows  in  skeleton  form  Fig.  50,  ready  for  lay- 
ing out  the  interurban  part  of  the  system.  With  the  main 
urban  system  we  need  not  concern  ourselves,  since  the  feed- 
ing system  would  be  developed  in  accordance  with  princi- 


IO6     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

pies  already  laid  down.  The  distance,  A  B,  being  ten  miles 
we  have  already  seen  that  to  deliver  an  assumed  maximum 
of  500  amperes  at  B  would  require  at  1 50  volts  total  drop, 
about  2,000,000  c.  m.  of  copper,  costing  about  $45,000. 
This  we  will  assume  to  be  based  on  a  dynamo  giving  at 
full  load  with  its  overcompounding  550  volts  in  accordance 
with  ordinary  practice.  The  voltage  at  the  motors  will 
then  occasionally  drop  to  400  volts,  certainly  the  extreme 
drop  that  could  be  tolerated.  We  have  already  seen  that 
by  boosting  to  750  volts  and  doubling  the  loss  in  the  line, 
the  copper  can  be  reduced  by  one-half.  At  the  same  time 
the  minimum  voltage  is  raised  to  about  450,  which  is  much 
more  satisfactory. 

Now  suppose  that  instead  of  doing  either  of  these 
things  we  say  to  ourselves,  ' '  These  standard  motors  of 
ours  are  intended  to  operate  on  500  to  550  volts  like  the 
generators,  let  us  make  them  do  it."  In  fact  these  stand- 
ard railway  motors  will  operate  beautifully  at  550  volts. 
Gear  them  so  as  to  get  the  full  advantage  of  this  voltage 
and  keep  down  the  current.  Without  any  allowance  for 
increased  efficiency  at  the  higher  voltage  the  mere  change 
of  the  running  voltage  at  maximum  load  from  400  to  550, 
leaving  other  things  the  same,  reduces  the  current  to  be 
transmitted  for  the  same  energy  from  500  amperes  to  364 
amperes.  Now  install  a  boosting  dynamo  as  before,  auto- 
matically holding  the  voltage  at  B  at  or  near  550  volts. 
Using  a  200  volt  booster  as  before,  we  can  allow  200  volts 
drop,  and  figuring  the  copper  on  this  basis  it  appears  that 
i,  183, ooo  c.  m.  will  do  the  work.  As  a  matter  of  fact 
there  would  be  an  additional  gain  of  nearly  ten  per  cent 
owing  to  higher  motor  efficiency. 

The  net  result  is  that  the  copper  needed  for  the  work 
at  500  volts  is  cut  in  half  while  the  loss  in  voltage  at  full 
load  is  twenty-six  per  cent  instead  of  forty  as  in  the  orig- 
inal booster  system  and  the  boosting  dynamo  itself  is  for 
seventy-five  kilowatts  instead  of  one  hundred  kilowatts. 

As  to  the  actual  arrangement  of  the  feeders,  for  a 
system  likely  to  involve  the  use  of  large  motor  units  and 


SPECIAL   METHODS   OF   DISTRIBUTION.  1  07 

high  speeds  the  author  prefers  a  decidedly  heavy  trolley 
wire  and  would  not  hesitate  in  this  case  to  employ  No.  ooo 
or  No.  oooo  trolley  wire,  putting  the  remainder  of  the  cop- 
per in  two  cables  of  about  450,000  c.  m.  each. 

These  feeders  may  be  well  arranged  as  shown  in  the 
dotted  lines  of  Fig.  59,  one  of  them  being  carried  right  on 
to  B  the  other  being  tapped  into  the  trolley  wire  at  a  few 
points.  The  station  A  is  capable  of  taking  care  at  the  in- 
creased voltage  on  a  long  stretch  of  the  trolley  wire  with- 
out any  taps  from  the  feeder,  since  a  No.  oooo  wire  has 
high  carrying  capacity.  Transposing  one  of  our  stock 
formulae 


13 

and  assuming  one  hundred  volts  drop,  a  No.  oooo  wire  can 
rarry  one  hundred  amperes  a  distance  of  over  three  miles 
unaided.  The  main  precaution  that  has  to  be  taken  is  to 
make  sure  that  when  a  load  at  B  is  forcing  the  boosting 
system  to  its  full  voltage,  a  car  may  not  be  caught  on  a 
dangerously  high  voltage  near  the  station.  Perhaps  the 
simplest  way  of  avoiding  this  contingency  is  to  cut  the 
trolley  wire  at  some  point  like  C  and  feed  the  section  next 
the  station  direct  from  the  generator  without  the  inter- 
vention of  the  booster.  If  the  conductivity  of  the  trolley 
wire  is  needed  up  to  this  point  for  the  general  transmission 
it  is  easy  to  reinforce  the  feeders  between  A  and  C  by  an 
equivalent  amount.  The  exact  treatment  of  such  a  case 
must  be  determined  by  the  relative  amounts  of  true  inter- 
urban  and  terminal  traffic. 

If  the  problem  we  have  been  considering  had  not  in- 
volved considerable  local  work  at  B,  but  only  interurban 
work  up  to  that  point,  it  perhaps  would  have  been  better  to 
operate  the  line  at  1000  volts,  using  two  motors  in  series. 
This  procedure  would  have  been  feasible  if  there  were,  as 
often  happens,  an  independent  railway  system  at  B.  It 
probably  would  not  be  often  desirable  to  continue  a  1000  volt 
system  through  a  city  for  general  service,  and  in  the  ab- 
sence of  a  substation  or  a  local  system  there  is  no  good 


108     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

way  of  obtaining  the  lower  voltage  desired.  The  three- wire 
system  may  sometimes  be  used  to  advantage  in  doing  the 
terminal  work  connected  with  a  high  voltage  interurban 
line.  In  conjunction  with  boosters  it  may  also  be  occasion- 
ally useful  in  working  a  long  and  heavily  loaded  double 
track  line.  Fig.  60  shows  this  arrangement,  which  it  will 
be  readily  seen  is  really  a  modified  five- wire  system.  The 
main  generators  would  then  operate  directly  an  ordinary 
three- wire  railway  system,  while  with  the  assistance  of  the 
boosting  dynamos  they  would  furnish  current  for  working 
a  heavy  suburban  or  interurban  line  in  the  manner  just 
described. 

Such  are  the  principal  devices  for  operating  extended 
railway  lines  from  a  single  power  station  without  any  trans- 


JJ50 


FIG.  60. 

formation  of  voltage.  They  are  easy  of  application  and 
fairly  economical,  although  the  voltages  dealt  with  are  not 
really  high  enough  for  the  purposes  to  which  they  are 
sometimes  applied.  There  is  a  steady  growth  of  long  lines 
which  cannot  be  economically  operated  by  any  of  these 
simpler  methods,  which  at  best  partake  something  of  the' 
nature  of  makeshifts.  The  time  comes  when  a  road  be- 
comes too  long  to  be  successfully  worked  from  a  single 
power  station  even  with  the  assistance  of  auxiliary  dyna- 
mos. A  choice  has  then  to  be  made  between  operating  inde- 
pendent power  stations  at  points  along  the  line,  and  sub- 
stations similarly  located  supplied  with  power  from  a 
single  generating  plant  by  the  means  usual  to  the  long 
distance  transmission  of  power.  The  principles  involved 
in  these  important  cases  it  is  now  cur  purpose  to  discuss. 


CHAPTER  V. 

SUBSTATIONS. 

From  what  has  already  been  said  it  is  evident  that 
even  with  the  assistance  of  boosters,  the  total  amount  of 
copper  required  for  the  distribution  of  power  over  consid- 
erable distances  rapidly  becomes  burdensome.  It  there- 
fore becomes  necessary  either  to  lessen  the  distance  of 
transmission  by  multiplying  generating  stations  or  to  adopt 
more  economical  means  of  transmission  than  is  to  be  found 
in  the  direct  supply  of  continuous  current  as  ordinarily 
employed.  In  either  case  it  is  necessary  to  consider  the 
conditions  of  economy  to  which  the  distribution  of  power 
from  several  working  centers  is  subject. 

In  practice  substation  working  takes  one  of  the  three 
following  forms:  i.  Auxiliary  stations  maintained  at 
various  points  of  an  extensive  network,  and  designed  to 
reinforce  a  main  station  in  the  supply  of  distant  districts. 
2.  Distributed  stations  essentially  separate  and  serving  to 
supply  consecutive  sections  of  a  line  or  network.  3.  Pure 
substations  effecting  local  supply  of  power  in  connection 
with  transmission  from  a  central  station. 

Into  one  or  another  of  these  classes  fall  with  more  or 
less  exactness  all  cases  of  multiple  centers  of  distribution. 
The  first  named  is  found  generally  in  large  urban  railway 
systems,  which  have  gradually  grown  beyond  the  effective 
reach  of  the  main  generating  station.  It  is  the  natural 
and  legitimate  outcome  of  extensive  growth.  The  finest 
example  of  such  practice  is  to  be  found  upon  the  tramway 
system  of  Boston,  Mass.  This  case  is  shown  in  Fig.  61. 
Here  A  is  the  central  Albany  Street  power  house  of  10,500 
k.w.  aggregate  output.  It  is  reinforced  by  six  auxil- 
iary stations — B  the  Allston  station  of  300  k.  w. ,  C  the 


110     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

East  Cambridge  station  of  3500  k.  w.,  D  the  East  Boston 
station  of  675  k.  w. ,  E  the  Charlestown  station  of  1600 
k.  w. ,  F  the  Dorchester  station  of  2000  k.  w.  and  G  the 
Harvard  station  of  3600  k.  w. 


aldenSq. 


Street  RaUway  Journal 


FIG.  61. 


Still  another  auxiliary  station  is  soon  to  be  erected. 
Each  of  these  stations  supplies  a  district  which  would 
otherwise  be  too  far  from  the  central  station  for  economical 
distribution,  and  tliey  are  at  the  same  time  so  intercon- 


SUBSTATIONS.  Ill 

nected  that  in  case  of  accident  to  one  the  others  can  carry 
on  its  load  with  a  fair  degree  of  efficiency.  This  mutual 
relation  is  important  in  that  it  permits  a  smaller  reserve 
capacity  than  would  be  necessary  were  the  stations  inde- 
pendent. For  example,  the  present  plant  in  the  Charlestown 
station  consists  of  two  800  k.  w.  generators  each  coupled 
direct  to  a  compound  condensing  Corliss  engine.  It  is  an 
ideal  plant  for  the  purpose,  but  as  a  separate  station  it 
would  have  too  few  units  for  safety  unless  one  of  the  pair 
should  be  virtually  held  as  a  partial  reserve. 

The  second  class  is  composed  in  the  main  of  inter- 
urban  roads  too  long  to  be  conveniently  supplied  from  a 
single  station.  In  such  cases  the  use  of  two  or  more  power 
stations  is  the  simplest  way  out  of  the  difficulty,  and  these 
stations,  having  similar  functions,  are  naturally  of  similar 
size  and  character,  and  so  distributed  as  to  supply  similar 
lengths  of  track  as  far  as  practicable.  The  interurban  sys- 
tem centering  in  Cleveland,  O.,  furnishes  a  good  instance 
of  such  practice.  This  is  shown  in  a  sketch  map  in  Fig.  62. 
It  consists  substantially  of  three  roads,  the  Akron,  Bedford 
&  Cleveland,  the  Cleveland  &  Elyria,  and  the  Cleveland, 
Painesville  &  Eastern.  The  first  mentioned  is  about  thirty 
miles  long  with  two  power  stations,  A  and  B,  of  the  figure. 
The  former  furnishes  current  for  six  miles  north  and  nine 
miles  south,  the  latter  nine  miles  north  and  five  and  a  half 
miles  south.  The  two  stations  are  each  of  500  k.  w.  capacity 
and  are  substantially  duplicates.  The  second  road  is  sev- 
enteen miles  long  and  has  also  two  power  stations,  C  and 
D.  Here  C,  of  about  the  same  size  as  A  and  B,  sends  cur- 
rents in  both  directions  while  D,  considerably  smaller, 
handles  the  section  of  line  nearest  the  Elyria  terminus. 
The  third  road  is  about  thirty  miles  long.  It  is  supplied 
with  power  from  the  Cleveland  end,  and  has  also  another 
power  station  at  E.  To  these  must  now  be  added  the 
Cleveland  &  Lorain  Railway,  a  fine  interurban  road  twen- 
ty-seven miles  long,  having  a  power  station  at  F  supplying 
the  line  between  I^orain  and  Rocky  River.  From  Cleve- 
land to  Rocky  River  the  cars  run  over  an  existing  line. 


112     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

The  track  is  laid  with  60  ft.  rails  and  following  the  sug- 
gestions made  in  this  chapter  the  two  400  k.  w.  generators 
are  designed  for  a  voltage  of  630  at  no  load  and  700  at  full 
load. 

Roads  of  this  character  can  readily  be  extended  by  in- 


FIG.  62. 


creasing  the  number  of  power  stations  and  using  boosters. 
Indeed  this  was  the  original  method  proposed  for  working 
long  lines  and  in  very  many  cases  may  still  be  the  best 
method,  at  least  until  there  has  been  further  development  in 
alternating  motors  for  railway  service.  It  is  interesting  to 
note  however  that  stations  A  and  B  are  equipped  with  com- 


SUBSTATIONS. 

posite  generators  fitted  to  deliver  alternating  or  continuous 
currents  or  both,  so  that  one  can  eventually  become  merely 
a  substation  to  transform  energy  received  from  the  other. 
At  present  both  stations  are  worked  in  the  ordinary  way. 

The  third  class,  true  substations,  is  just  coming  into 
existence,  as  it  is  a  result  of  the  extension  of  interurbaff 
work.  It  includes  all  cases  of  power  transmission  to  dis- 
tributed stations  and  at  present  involves  the  use  of  motor 
generators  or  their  equivalent.  Whenever  alternating 
motors  for  railway  service  shall  be  thoroughly  worked 
out,  this  class  of  substation  work,  freed  from  the  present 
necessity  of  rotating  apparatus,  will  be  likely  to  lead  the 
others  in  importance.  At  present  it  is  being  used  rather 
extensively  as  a  substitute  for  the  second  class  of  sub- 
station. 

The  first  example  of  this  substation  work  in  connec- 
tion with  power  transmission  was  the  Lowell  (Mass.)  one 
shown  in  Fig.  63.  The  total  length  of  the  line  is  nearly 
fifteen  miles  and  all  the  power  is  supplied  from  the  main 
power  station  A,  which  is  equipped  with  four  100  k.  w. 
composite  generators  giving  either  three  phase  or  continu- 
ous current.  A  bank  of  raising  transformers  gives  a  5500 
volt,  three  phase  current  on  the  line.  This  is  transmitted 
to  the  two  substations  B,  nine  miles  from  A,  at  Ayer's 
Mills,  and  C,  fifteen  miles  from  A  at  Nashua,  N.H.  These 
substations  are  duplicates.  Each  contains  two  75  k.  w.  ro- 
tary transformers,  together  with  the  necessary  switchboards 
and  bank  of  reducing  transformers.  Station  B  was  started 
first  and  supplies  the  middle  section  of  the  line,  while  the 
Lowell  end  forms  part  of  the  regular  street  railway  system 
and  is  fed  from  A.  C,  the  Nashua  substation,  feeds  the 
terminal  portion  of  the  line  and  provides  the  local  service  in 
Nashua,  replacing  a  steam  power  station.  At  A,  the  gen- 
erators are  operated  regularly  in  parallel  and  in  each  sub- 
station the  rotary  transformers  are  run  in  parallel. 

The  details  of  some  of  these  typical  substations  will 
be  taken  up  later;  for  the  present  purpose  it  is  enough 
to  outline  them  sufficiently  to  emphasize  the  economic 


/1 4     POWfcR   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

conditions  on  which  they  depend.  These  are  obviously 
different  in  the  different  classes,  but  in  all  we  have  to  deal 
with  the  same  general  circumstances. 

The  time  comes  in  the  growth  of  a  great  urban  street 
railway  system  or  the  development  of  long  interurban 
lines,  when  the  cost  of  transmission  of  the  necessary  power 
becomes  very  burdensome  on  account  of  the  long  distances. 


NASHUA 


M      A 


Street  Railway  Journal 


OWELL 


FIG.  63. 


Something  has  to  be  done,  but  to  define  the  particular 
thing  which  is  best  under  the  circumstances  is  generally 
far  from  an  easy  task.  The  operation  of  substations  of 
any  kind  means  usually  an  increased  cost  of  power  de- 
livered at  the  station  switchboard,  incurred  in  order  to 
save  a  heavy  expense  in  power  distribution. 

Minimum  total  cost  of  power  is  the  thing  to  be  sought. 
If  generated  in  a  single  central  station  it  can  be  delivered 
at  the  switchboard  cheaply,  but  the  total  cost  per  kilowatt 
actually  used  may  be  quite  high.  On  the  other  hand  if 
the  power  is  generated  in  separate  substations  the  cost  of 


SUBSTATIONS.  115 

generation  is  raised  and  that  of  distribution  lowered.  In 
substations  of  the  third  class,  the  original  cost  of  genera- 
tion is  low,  but  the  transmission  of  power  to,  and  the 
maintenance  of,  the  substations  has  to  be  balanced  against 
the  cost  of  distribution  from  the  main  station  direct,  and 
the  cost  of  generating  at  separate  stations. 

This  balancing  of  costs  involves  very  nice  discrimina- 
tions and  deals  with  somewhat  uncertain  factors.  The 
true  cost  of  electric  power  itself  is  not  easy  to  estimate, 
and  actual  data  from  existing  stations  are  often  rendered 
valueless  by  disingenuous  bookkeeping.  There  is  a  great 
difference  between  the  cost  of  power  computed  from  fuel 
and  labor  alone,  as  is  often  done  by  those  who  like  to  de- 
ceive themselves,  and  the  cost  with  all  the  items  of  inter- 
est, repairs  and  depreciation  relentlessly  footed  up.  It  is 
not  unusual  to  find  the  item  of  depreciation  deliberately 
neglected  in  computing  the  cost  of  power  and  in  other 
estimates.  Street  railways  have  been  particularly  prone 
to  this  sort  of  financial  juggling — it  is  so  convenient  to  in- 
crease the  capital  account  for  ' '  improvements ' '  instead  of 
withholding  dividends  really  unearned  or  shouldering  a 
genuine  deficit.  Without  discussing  this  question  of 
financial  morality,  we  cannot  too  forcibly  remind  the  en- 
gineer not  to  deceive  himself  and  the  manager  that  if  the 
present  trend  of  legislation  and  * '  labor  reform  ' '  continues 
there  is  likely  to  come  a  dreadful  day  of  reckoning  in  which 
a  sinking  fund  will  be  sorely  needed. 

To  determine  the  conditions  of  economy  that  govern 
the  establishment  of  substations,  it  is  first  necessary  to 
know  the  probable  cost  of  electric  power  in  stations  of  dif- 
ferent sizes  and  kinds.  This  is  not  easy  to  estimate  in 
general,  but  can  be  gotten  at  with  fair  accuracy  for  any 
given  set  of  conditions  as  to  cost  of  plant,  coal,  labor  and 
so  forth.  In  small  plants  the  labor  item  is  disproportion- 
ately large  and  the  general  efficiency  less  than  in  large 
ones.  On  the  other  hand  in  plants  of  1000  k.w.  output 
and  over  the  labor  item  remains  proportionately  nearly  the 
same  as  the  plant  increases  in  size,  and  the  efficiency  rises 


Il6     POWER   DISTRIBUTION  POR   ELECTRIC   RAILROADS. 

very  slowly.  Much  too,  depends  on  the  average  output  of 
the  station  compared  with  its  full  capacity,  i.  e.,  upon  the 
point  of  output  at  which  the  engines  and  dynamos  are 
worked. 

To  take  a  cwjcrete  case  on  which  to  base  our  calcula- 
tions, let  us  investigate  the  variation  of  cost  of  power  with 
capacity  of  station,  on  the  following  assumptions.  Plant 
of  condensing  Corliss  engines  or  compound  condensing 
high  speed  engines,  supplied  with  modern  accessories  and 


1000  1500 

CAPACITY   IN   K.W. 

FIG.  64, 


Street  Ry  .Journal, 


furnished  with  steam  by  water  tube  boilers.  Dynamos 
direct  belted  or  direct  coupled,  of  best  modern  types  and 
supplied  with  first  class  station  equipment.  Plain,  sub- 
stantial, brick  power  house  and  stack.  Coal  $3.00  per  long 
ton  delivered  in  coal  bins.  Interest  and  depreciation  are 
grouped  together  at  ten  per  cent  per  annum. 

Taking  into  account  labor  at  ordinary  rates,  and 
assuming  a  service  of  from  eighteen  to  twenty  hours  per 
day,  one  can  compute  the  cost  of  power  with  tolerable 


SUBSTATIONS.  117 

exactness.  The  results  are  shown  in  Fig.  64.  Three 
curves  are  given  showing  the  cost  per  kilowatt  hour  for 
average  outputs  of  forty,  fifty  and  seventy  per  cent  of  the 
total  nominal  working  capacity.  Ordinary  care  is  sup- 
posed to  be  exercised  in  keeping  unnecessary  machines 
out  of  service. 

These  results  are  higher  than  those  often  claimed,  but 
they  check  quite  closely  with  several  independent  estimates 
made  by  different  engineers  and  also  with  results  obtained 
from  actual  practice  in  modern  plants,  making  the  neces- 
sary corrections  for  cost  of  fuel,  etc. 

A  casual  inspection  of  Fig.  64  shows  several  important 
facts  very  plainly.  First,  under  500  k.  w.  capacity  the  cost 
of  power  per  kilowatt  increases  very  rapidly  as  the  station 
decreases  in  size.  For  example,  following  the  70  per  cent 
curve,  the  cost  per  kilowatt  hour  in  a  station  of  500  k.  w 
is  1.8  cts.,  rising  to  2.6  cts  in  a  250  k.  w.  station. 

Second,  above  1000  k.  w.  output  the  cost  decreases 
quite  slowly  with  the  output,  and  above  2000  k.  w.  it 
would  become  almost  uniform  finally  reaching  a  point  at 
which  further  increase  in  size  would  not  decrease  the  cost 
of  power  per  k.  w.  h.  At  what  capacity  the  curves  thus 
become  asymptotic  is  somewhat  uncertain,  but  at  present 
it  seems  doubtful  whether  any  increase  beyond,  say,  20,000 
k.  w.  would  lead  to  lessened  cost.  It  is  quite  certain  that 
several  stations  now  building  are  beyond  the  critical 
capacity. 

Hence,  generally,  when  a  plant  is  of  such  magnitude 
that  sub  or  auxiliary  stations  of  1000  k.  w.  or  more  can  be 
employed,  the  cost  per  kilowatt  hour  at  such  stations  will 
vary  little  from  the  cost  at  the  main  station  and  most  of 
the  saving  in  feeder  copper  will  be  pure  gain.  On  the 
other  hand  if  substations  need  but  two  or  three  hundred 
kilowatt  capacity  they  can  be  operated  only  at  a  cost  suffi- 
cient to  balance  a  large  expenditure  for  copper.  To  take 
a  concrete  case,  compare  the  cost  of  power  from  a  500  k.w. 
station  with  that  from  two  250  k.  w.  substations,  as  given  by 
the  70  per  cent  curve  assuming  the  day's  run  to  be  20  hours. 


Il8    POWKR   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

At  the  500  k.w.  station  the  cost  would  be  1.8  cts.  per  kilo- 
watt hour.  At  250  k.w.  mean  output  the  total  yearly  cost 
of  power  would  be  $32,850.  Deriving  the  same  yearly 
output  from  two  250  k.w.  stations  the  cost  would  be 
$47,450,  showing  a*  yearly  balance  of  $14,600  in  favor  of 
the  single  station,  to  offset  the  smaller  cost  of  feeders  and 
the  greater  efficiency  of  distribution  possible  with  the  two 
stations.  It  is,  therefore,  easy  to  get  a  rough  idea  of  the 
relative  cost  of  feeding  a  long  line  from  a  single  central 
station  and  from  a  pair  of  stations  symmetrically  placed. 
A  B  (Fig.  65)  be  a  line  thirty  miles  in  length  and  re- 


FIG.  65. 

quiring  a  total  average  output  of  250  k.w.  with  a  capacity 
for  500  k.w.  It  is  cheaper  to  feed  it  from  a  single  station, 
C,  at  the  middle  of  the  line  or  from  a  pair  of  stations,  D 
and  E,  each  centrally  located  on  a  half  of  the  main  line? 

We  may  assume  the  current  in  either  case  to  be  500 
amperes  and  the  average  drop  fifty  volts.  With  a  single 
station,  taking  the  average  distance  of  transmission  as  half 
the  extreme  distance  in  either  direction,  the  length  of  the 
transmission  would  be  about  40,000  ft. 

Reverting  now  to  our  weight  formula  and  writing 
3  X  14  =  42  as  the  constant  we  have 


K 

And  applying  this  formula  to  our  data  we  find  that  for 
feeder  copper  for  the  given  loss  there  would  be  required 
336  tons  of  wire  and  cable  costing  in  the  neighborhood  of 
$94,000.  On  the  other  hand  if  two  generating  stations  at 
D  and  K  are  employed  the  average  distance  of  transmission 
would  fall  to  about  20,000  'ft.,  and  since  the  weight  of 
copper  required  varies  directly  as  the  square  of  the  dis- 
tance, there  will  be  required  for  the  new  state  of  things 
eighty-  four  tons  of  feeder  copper  costing  about  $23,500. 


SUBSTATIONS.  IIQ 

The  net  saving  in  cost  of  copper  is  then  $60,500.  In  lay- 
ing out  the  feeders  for  an  actual  road  these  figures  would 
doubtless  be  somewhat  modified  by  the  conditions  of  traffic, 
but  the  general  condition  is  a  saving  of  about  $60,000  in 
first  cost  as  against  an  extra  yearly  expenditure  of  over 
$14,000  in  power.  In  the  average  case  there  would  be  a 
strong  tendency  to  use  the  two  stations.  There  would  be 
just  so  much  less  money  to  raise,  the  $14,000  would 
dwindle  under  the  deft  fingers  of  the  bookkeeper  and 
growth  of  the  road  would  soon  compel  the  use  of  two  sta- 
tions anyway.  On  the  other  hand  the  skillful  use  of  a 
boosting  system  might  cut  the  extra  expenditure  in  two 
and  the  single  plant  would  be  by  far  the  more  economical. 

The  questions  regarding  probable  growth  involve  very 
close  judgments,  and  local  conditions,  such  as  cost  of  real 
estate  and  nearness  to  coal  and  water  supply,  may  often 
properly  turn  the  scale  one  way  or  the  other.  As  between 
a  single  1000  k.  w.  plant,  and  two  500  k.  w.  stations,  there 
would  be  no  doubt  as  to  the  propriety  of  installing  the 
latter,  while  with  a  less  aggregate  than  500  k.  w.  capacity, 
the  single  station  would  very  often  be  preferable.  The 
longer  the  line  and  the  greater  the  aggregate  output  the 
greater  the  advantage  of  using  several  generating  stations. 
In  most  lines  of  twenty-five  or  thirty  miles  in,  length  local 
or  terminal  demands  for  power  will  indicate  the  use  of  a 
pair  of  stations  by  raising  the  aggregate  power  or  increas- 
ing the  average  distance  to  which  power  would  have  to  be 
transmitted  from  a  single  station.  Now  and  then  how- 
ever exactly  the  sort  of  conditions  set  forth  in  the  estimate 
are  encountered  and  a  single  station  is  desirable.  In 
strictly  interurban  work  the  suburban  traffic  near  the  ends 
of  the  line  is  almost  certain  to  make  the  substation  plan 
the  cheaper.  vSuch  is  naturally  the  case  in  the  roads 
shown  on  the  map  (Fig.  62). 

On  very  long  lines  the  question  is  still  further  com- 
plicated, for  the  distances  may  readily  be  too  great  to  work 
easily  even  with  two  stations,  and  if  the  traffic  is  not  unu- 
sually great  the  output  of  each  station  may  be  rather  small 


£20    POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

and  intermittent,  raising  the  cost  per  kilowatt  hour  by  a  con- 
siderable amount.  This  amount  differs  greatly  according 
to  the  circumstances  of  load,  but  we  can  get  a  rough  indi- 
cation by  making  the  supposition  that  the  station  in 
question  is  actually  delivering  power  but  half  of  the  time 
and  on  the  average  at  half  capacity. 

Under  such  circumstances  the  cost  per  kilowatt  hour 
will  be,  in  stations  up  to  500  k.  w.  capacity,  fifteen  to 
twenty  per  cent  in  excess  of  the  cost  on  the  basis  of  a 
twenty  hour  run  at  the  same  proportional  load. 

This  class  of  work  is  that  in  which  the  electrical,  trans- 
mission of  power  at  high  voltage  to  the  substations  is  most 
tempting.  The  substations  on  this  plan  are  comparatively 
cheap  and  the  labor  item  is  small,  while  the  cost  of  copper 
for  the  transmission  line  is  quite  trivial.  Nevertheless 
these  cases  must  be  very  closely  scanned,  for  power  trans- 
mission from  a  steam  plant  in  fairly  large  units,  to  compete 
with  steam  power  at  cost  and  economically  generated,  has 
still  a  rather  narrow  margin  for  profit. 

With  this  glimpse  at  the  general  conditions  of  economy 
we  may  profitably  pass  to  concrete  consideration  of  the 
three  classes  of  substation  working  already  mentioned. 

While  the  Boston  tramway  already  mentioned  is  the 
best  example  of  auxiliary  station  practice,  it  is  not  yet 
homogeneous,  as  much  of  the  earlier  equipment  is  still  in 
use  and  the  whole  system  is  the  result  of  both  agglomera- 
tion and  extension.  The  Charlestown  substation  is  one 
of  the  best  and  latest  examples  of  its  kind  and  will  re- 
pay a  little  study  in  detail.  Fig.  66  shows  an  interior  view 
of  this  station  and  Fig.  '67,  the  plan.  The  power  plant 
consists  of  two  cross  compound  condensing  Allis-  Corliss  en- 
gines, each  forty-eight  inches  stroke,  with  cylinders  twenty- 
six  inches  and  fifty  inches  in  diameter.  Each  engine  runs 
at  ninety  revolutions  per  minute,  is  direct  coupled  to  an 
800  k.  w.  G.  E.  generator  and  is  provided  with  a  steel  fly- 
wheel built  up  of  rolled  plates  and  weighing  a  little  over 
forty  tons.  As  the  peripheral  velocity  of  these  wheels  is 
nearly  6000  ft.  per  minute,  the  plate  construction  is  most 


SUBSTATIONS, 


121 


66. 


122     POWER   DISTRIBUTION   FOR  ELECTRIC  RAILROADS. 


FIG.  67. 


SUBSTATIONS.  123 

important.  The  choice  of  compound  instead  of  triple  ex- 
pansion engines  was  probably  a  wise  one,  since  while  the 
latter  are  a  trifle  more  economical  at  full  load,  they  are  less 
able  to  cope  efficiently  with  great  variations  of  load,  such 
ajL  met  in  railway  work.  Only  in  the  largest  stations  can 
they  be  so  worked  as  to  take  full  advantage  of  their  low 
steam  consumption.  The  engines  are  separable,  so  that  in 
an  emergency  either  the  high  or  low  pressure  cylinder  can 
be  worked  as  a  simple  engine. 

The  boilers  are  Babcock  &  Wilcox  designed  to  supply 
steam  at  pressures  as  high  as  1 80  Ibs. 

The  arrangement  of  the  station,  as  a  glance  at  Fig. 
67  will  show,  is  exceptionally  good.  The  whole  plant 
is  very  compact,  the  piping  between  boilers  and  engines  is 
very  short,  and,  what  is  rather  unusual,  the  switchboard  is 
where  it  ought  to  be,  close  to  the  other  apparatus,  on  the 
same  level  and  perfectly  accessible.  The  accessories  are  very 
complete  and  the  whole  plant  is  a  fine  example  of  the  most 
advanced  modern  practice.  Almost  the  only  question  that 
could  be  raised  concerning  it  would  be  the  desirability  of 
using  vertical  marine  type  engines,  which  are  of  equally 
high  efficiency,  slightly  higher  speed  and  take  up  much 
less  floor  space.  For  auxiliary  station  work  with  a  greater 
number  of  power  units  or  for  use  in  a  principal  station  there 
is  much  to  be  said  in  their  favor,  but  in  the  case  in  hand, 
where  ground  space  is  not  relatively  very  valuable,  and 
only  two  great  units  were  to  be  installed,  honors  are  pretty 
even,  with  this  advantage  on  the  side  of  the  horizontal 
engine  that  the  cylinders  can  be  worked  independently 
with  far  greater  ease  than  in  the  case  of  a  vertical  en- 
gine. 

It  is  altogether  probable  that  power  can  be  generated 
in  this  station  quite  as  cheaply  as  in  the  main  Albany  Street 
station,  as  the  latter  is  not  yet  completely  remodeled,  and 
the  actual  result  of  a  year's  operation  tends  to  confirm 
this  judgment.  In  any  event  a  cursory  comparison 
with  our  curves  of  cost  shows  that  the  output  of  the 
Charlestown  station  is  great  enough  to  bring  it  to  a  very 


T24     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

good  point.  If  properly  handled  it  should  produce  power 
at  a  price  not  more  than  one  mill  per  kilowatt  hour  greater 
than  the  best  that  can  be  done  in  the  principal  station. 
This  difference  is  so  small  as  to  be  more  than  offset  by  the 
mere  loss  in  energy  that  would  be  incurred  in  transmitting 
the  power  concerned  from  the  main  station  without  involv- 
ing an  overwhelming  expenditure  for  copper.  A  loss  of 
ten  per  cent  in  transmission  would  wipe  out  the  difference 
and  involve  the  expenditure  of  many  thousand  dollars  in 
copper  to  boot.  A  general  idea  of  the  economy  of  this 
and  other  auxiliary  stations  can  be  had  as  follows: 

Given  1000  k.  w.  to  be  delivered  an  average  distance 
of  10,000  ft.  from  the  principal  station  for  twenty  hours 
per  day,  and  a  difference  in  cost  of  generation  of  one  mill 
per  kilowatt  hour  between  principal  and  auxiliary  stations. 
Is  it  cheaper  to  run  the  auxiliary  stations  or  transmit  the 
power  ? 

The  amount  of  power  under  consideration  will  cost  at 
the  substation  $20  per  day  more  than  at  the  principal 
station — $7300  per  year.  To  offset  this  we  have  the  in- 
terest on  the  copper  necessary  for  transmission  and  the  loss 
incurred  in  the  transmission.  Allowing  five  per  cent  loss 
in  transmission  we  have  a  net  loss  of  loook.  w.  h.  per  day, 
costing  not  less  than  $10  and  in  most  stations  more. 

The  copper  necessary  for  the  feeder  line  at  five  per  cent 
loss  would  be  about  168  tons  not  including  the  insulation, 
costing  in  place  not  less  than  $50,000.  At  ten  percent  for 
interest,  depreciation,  repairs  and  miscellaneous  charges, 
the  annual  charge  would  be  $5000  per  year,  leaving  an 
annual  balance  of  $1350  in  favor  of  the  auxiliary  station 
method. 

This  advantage  would  exist  pro  rata  for  smaller  power 
transmitted  so  long  as  the  difference  of  one  mill  per  kilowatt 
hour  might  hold.  With  a  difference  proportionately  so  small 
one  may  say  that  auxiliary  stations  will  begin  to  pay  at  a 
radius  of  from  a  mile  and  a  half  to  two  miles  from  the 
principal  station  and  at  greater  distances  become  rapidly 
more  and  more  profitable. 


SUBSTATIONS.  125 

/ 

Unless  some  one  locality  shows  marked  advantage  as 
a  point  for  the  cheap  production  of  power,  there  is  little 
cause  for  a  principal  station,  for  a  better  distribution  can  be 
had  from  two  or  more  stations  of  nearly  the  same  output, 
each  taking  care  of  its  own  portion  of  the  general  network. 
This  is  evident  from  two  separate  considerations.  First, 
the  cost  of  power  per  kilowatt  hour  is  less,  and  second,  the 
stations  can  reinforce  each  other  to  better  advantage  when 
they  are  tolerably  uniform.  If  separate  stations  are  to  be 
used  at  all,  the  whole  district  is  on  the  average  better 
served  in  this  way.  These  matters  however  usually  settle 
themselves  in  the  process  of  natural  growth  without  oppor- 
tunity for  theoretical  adjustment. 

In  distributed  stations  for  interurban  and  long  distance 
work,  approximate  equality  is  the  rule  except  as  local  sub- 
urban traffic  may  call  for  separate  treatment. 

The  two  stations  of  the  Akron,  Bedford  &  Cleveland 
Railway  already  mentioned  are  thoroughly  typical  of  mod- 
ern practice  in  this  respect.  Fig.  68  shows  the  interior  of 
the  Cuyahoga  Falls  substation  of  this  road.  It  is  specially 
interesting  as  being  adapted  for  transformation  into  a 
power  transmission  station,  if  growth  of  the  road  should 
render  such  a  change  desirable  at  some  future  time.  The 
generators,  as  already  mentioned,  are  composite  machines, 
supplied  with  the  ordinary  commutator  and  also  with 
a  set  of  outboard  collecting  rings  to  deliver  from  the  arm- 
ature winding  polyphase  currents  which  would  otherwise 
be  commutated  in  the  ordinary  way  and  sent  out  upon  the 
line  as  continuous  current.  Kach  machine  is  of  250  k.  w. 
capacity  and  delivers  either  continuous  current  at  500  volts 
or  alternating  currents  at  380  volts  and  3800  alternations 
per  minute.  Within  reasonable  limits  both  kinds  of 
current  can  be  delivered  at  once.  Although  at  present 
the  only  use  of  the  alternating  current  is  for  a  compara- 
tively trivial  amount  of  lighting,  by  installing  a  transmis- 
sion line  with  raising  and  reducing  transformers  it  becomes 
an  easy  matter  to  exchange  power  between  the  two  stations, 
in  case  of  accident  to  either  of  the  steam  plants  or  to  trans- 


SUBSTATIONS.  127 

mit  all  the  power  to  the  Bedford  station,  in  case  the  Cuya- 
hoga  Falls  plant  should  be  operated  by  water  power.  And  in 
case  it  should  prove  desirable  these  same  convenient  gener- 
ators could  supply  polyphase  current  to  the  trolley  line 
through  the  medium  of  static  transformers.  The  polyphase 
motor  has  much  to  commend  it  for  railway  service  as  we 
shall  see  later,  and  to  be  prepared  is  to  be  on  the  safe  side. 

As  regards  the  general  design  of  the  station  in  ques- 
tion, it  is  good.  The  Westinghouse  composite  generators 
lose  no  efficiency  by  the  addition  of  collecting  rings,  and 
direct  belting  to  a  Corliss  engine  is,  with  the  exception  of 
direct  coupling,  as  efficient  a  method  of  operation  as  could 
be  desired.  And  direct  coupling  to  composite  generators 
involves  great  practical  difficulties  at  ordinary  frequencies, 
as  will  be  explained  in  the  discussion  of  alternating  appa- 
tus  and  methods. 

As  to  the  economy  of  the  arrangement  of  stations 
adopted  in  the  case  of  this  road,  it  is  quite  safe  to  say  that 
the  distances  involved  and  the  terminal  conditions  demand 
the  use  of  two  stations  rather  than  one,  and  each  station  is 
sufficiently  large  to  ensure  tolerably  economical  production 
of  power. 

Of  the  possibility  of  using  one  station  as  the  generat- 
ing point  and  transmitting  power  to  the  other  we  will 
speak  later  in  discussing  special  substations. 

Roads  like  the  Akron,  Bedford  &  Cleveland,  how- 
ever, can  very  frequently  be  best  operated  without  recourse 
to  special  methods  of  power  transmission,  particularly  if 
the  working  voltage  is  carried  somewhat  above  500  volts, 
as  it  should  be.  It  should  be  noted  that  as  regards  the 
best  type  of  substation  working  these  interurban  roads 
stand  in  a  position  quite  different  from  that  occupied  by 
the  extension  of  similar  methods  to  long  distance  traffic  at 
high  speeds,  such  as  has  often  been  suggested  and  will 
probably  be  tried  ere  long.  The  interurban  road  has  rela- 
tively more  trains  and  more  stopping  places,  thus  produc- 
ing a  more  uniform  call  for  power  than  would  be  found  in 
an  electric  express  service.  Hence  each  substation  would 


128     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS, 

have  a  better  load  factor  and  more  continuous  service,  ren- 
dering it  more  easy  economically  to  run  separate  generat- 
ing stations.  When  the  service  in  any  part  of  a  road  is 
decidedly  discontinuous  and  gives  a  poor  load  factor,  that 
substation  will  give  the  best  economy  which  has  the  lowest 
fixed  charges  for  interest,  depreciation  and  labor.  Hence 
in  this  class  of  work  power  transmission  with  true  substa- 
tions, is  likely  to  give  better  results  than  independent  gen- 
erating stations.  Coming  now  again  to  this  class  of  true 
substation,  the  only  well  developed  example  is  found  in  the 
pioneer  power  transmission  plant  of  the  Lowell  &  Sub- 
urban Electric  Railway  running  from  Lowell,  Mass.,  to 
Nashua  a  distance  of  nearly  fifteen  miles.  Fig.  63  shows 
a  sketch  map  of  the  route.  The  first  step  was  the  trans- 
mission of  power  from  the  Lowell  generating  station,  A,  a 
little  over  nine  miles  to  B,  the  substation  at  Ayer's  Mills. 
A  little  later  the  generating  station  which  had  for  some 
time  done  service  at  Nashua  was  shut  down  and  replaced 
by  a  substation,  C,  fed  from  the  transmission  line  from 
Lowell.  The  need  of  this  terminal  substation  was  largely 
due  to  the  local  traffic  in  Nashua  which  is  a  place  of  some 
20,000  inhabitants;  and  a  heavy  summer  suburban  traffic 
extending  from  Lowell  to  a  pretty  lake  and  picnic  ground 
five  miles  north  called  for  ample  power  in  the  initial  sec- 
tion of  the  road.  Hence  power  was  transmitted  direct  to 
Nashua  for  the  load  there  and  also  to  an  intermediate  point 
which  could  supply  the  line  in  the  intermediate  section 
and  help  out  the  suburban  loads  at  each  terminus. 

The  generating  station  in  Lowell  is  common  to  the 
local  service  of  the  railway  line  and  to  the  transmission 
apparatus  proper,  which  was  added  when  the  long  distance 
line  was  undertaken. 

The  generating  apparatus  for  the  transmission  plant 
consists  of  four  100  k.w.  composite  generators  delivering 
either  direct  current  at  500  to  550  volts  or  three  phase  cur- 
rent at  about  320  volts.  In  this  case  the  three  phase  side 
only  is  in  regular  use,  and  the  current  is  transformed  in  a 
bank  of  substation  raising  transformers  to  a  pressure  of 


SUBSTATIONS. 


T2Q 


about  5500  volts,  at  which  it  is  transmitted  to  Ayer's  Mills 
and  to  Nashua.  The  frequency  of  the  three  phase  current 
is  about  thirty  complete  cycles  per  second — 3600  alterna- 
tions per  minute. 

The  four  generators  are  habitually  operated  in  parallel 
as  is  the  case  with  many  of  the  recent  polyphase  stations, 


FIG.  69. 

and  the  whole  plant  from  end  to  end  is  substantially  in 
parallel.  The  use  of  composite  generators  in  this  case 
seems  to  be  somewhat  unnecessary,  as  there  is  little 
reason  to  suppose  that  they  will  ever  be  diverted  from 
their  present  function  to  supply  an  extra  demand  for  con- 
tinuous current.  The  generators,  too,  are  belted  to  a 
common  shaft  instead  of  being  direct  belted  or  coupled. 
Altogether  the  generating  plant  could  have  been  decidedly 
improved  by  more  specialization.  On  the  other  hand  the 
substations  are  well  planned.  That  at  Ayer's  Mills  is  a 
compact  frame  building  divided  into  two  rooms.  One  of 
these  contains  the  bank  of  reducing  transformers  and  the 


130     POWER  DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

high  tension  switches  and  accessory  apparatus,  including  a 
little  direct  current  motor  for  furnishing  the  air  blast  which 
is  used  to  facilitate  dissipation  of  heat  from  the  transformers. 
Fig.  69  shows  the  interior  of  this  transformer  room.  The 
other  room  is  devoted  to  the  two  seventy-five  kilowatt  ro- 
tary converters  that  form  the  power  equipment,  together 
with  the  low  tension  three  phase  switchboard  and  the  rail- 
way switchboards  for  the  continuous  current  side  of  the 


FIG.  70. 

machines.  This  pair  of  rotary  converters  is  well  shown 
in  Fig.  70.  These  machines  have  proved  to  be  singularly 
convenient,  being  highly  efficient,  capable  of  enduring 
severe  overloads  without  difficulty,  and  generally  quite 
unexceptionable  in  their  performance. 

The  Nashua  substation,  C,  was,  so  far  as  apparatus  is 
concerned,  practically  a  duplicate  of  that  at  Ayer's 
Mills. 


SUBSTATIONS.  131 

This  lyO well- Nashua  line  is  hardly  long  enough  to 
give  power  transmission  its  full  measure  of  economy.  If 
this  line  were  to  be  considered  by  itself  it  would  be  an 
open  question  whether  the  work  could  not  have  been  done 
quite  as  economically  by  a  carefully  planned  booster  sys- 
tem, retaining  the  Nashua  generating  station.  In  case  of 
considerable  extension  either  beyond  Nashua  or  in  some 
other  direction,  the  transmission  plant  will  rise  to  its  full 
importance. 

As  regards  the  economy  of  substations  so  constituted 
the  case  is  somewhat  as  follows  :  without  the  transmis- 
sion the  items  to  be  considered  would  be  the  loss  of  energy 
and  the  cost  of  distributing  the  power  generated  in  the 
ordinary  way  at  one  or  more  stations.  On  the  other  hand 
would  be  the  cost  of  the  transmission  line  and  apparatus,  the 
energy  lost  therein,  and  the  cost  of  building,  maintaining 
and  operating  the  substations  themselves.  Substations  with 
rotary  converters  or  equivalent  apparatus  do  not,  it  is  true, 
require  a  large  amount  of  labor  in  their  operation.  But 
they  do  require  the  constant  attention  of  one  or  more  dynamo 
tenders,  and  the  same  general  care  that  would  have  to  be 
given  to  the  electrical  part  of  a  generating  station  of  sim- 
ilar capacity.  In  this  connection  it  is  interesting  to  note 
that  the  rotary  transformers  at  Nashua  have  recently  been 
moved  to  Ayer's  Mills,  and  the  line  is  now  operated  with 
a  single  substation.  The  use  of  storage  battery  substa- 
tions has  recently  become  rather  common  and  among 
others  a  typical  example  has  been  installed  in  connection 
with  one  of  the  suburban  lines  forming  a  part  of  the  Phil- 
adelphia, Pa. ,  electric  railway  system. 

This  particular  station  however,  serves  in  the  main 
merely  as  a  voltage  regulator,  and  is  in  so  far  a  makeshift 
that  no  general  results  of  value  can  be  derived  from  the 
somewhat  favorable  results  there  obtained. 

As  &  local  source  of  energy  transmitted  from  a  central 
station  the  storage  battery  is  rather  inefficient,  high  in  first 
cost,  and  subject  to  considerable  depreciation.  Its  chief 
merit  is  its  steadying  effect  on  the  load  of  the  central  sta- 


132     POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

tion.  The  efficiency  of  the  battery  in  point  of  energy 
under  favorable  conditions  may  be  taken  as  high  as  80  per 
cent,  at  least  10  per  cent  less  than  the  efficiency  of  a  rotary 
transformer,  while  it  costs  nearly  twice  as  much  per  kilo- 
watt of  capacity  and  has  certainly  a  higher  rate  of  de- 
preciation. 

Furthermore  it  requires  about  the  same  amount  of 
attention.  Whether  any  probable  improvement  in  the  load 
factor  of  the  main  generating  station  can  overbalance  these 
disadvantages,  save  in  small  stations,  is  very  doubtful. 

In  modern  electric  railway  practice  the  load  is  far 
more  uniform  than  is  generally  supposed  and  the  condi- 
tions of  economy  are  better.  For  example  in  the  Dorchester 
substation  of  the  Boston  tramways  the  average  daily  load 
ranges  from  70  to  75  per  cent  of  the  full  load  of  2000  k.  w. 
and  the  total  consumption  of  water  per  k.  w.  h.  is  18  to  20 
Ibs.  This  result,  for  compound  condensing  engines,  leaves 
but  a  small  margin  for  improvement  by  the  use  of  any 
device  for  steadying  the  load. 

It  is  quite  safe  to  say  that,  in  a  large  system,  battery 
substations,  large  or  small,  are  less  economical  than  sub- 
stations with  rotary  converters. 

In  the  Philadelphia  case  just  mentioned  the  battery 
substation,  with  a  maximum  permissible  output  of  500 
amperes,  cost  including  the  building,  $25,000.  This  is 
about  twice  the  cost  of  a  rotary  converter  station  for  the 
same  output,  requiring  no  more  attention  and  having  a 
lower  rate  of  depreciation  than  the  battery. 

In  charging  the  battery  a  booster  has  to  be  used  at 
the  power  house,  and  it  is  a  question  whether  a  properly 
designed  booster  system  without  the  battery  would  not 
have  served  the  same  purpose  quite  as  well  at  a  much 
lower  cost. 

It  is  however  probable  that  on  an  extensive  system 
with  a  moderate  and  wandering  load,  storage  battery  sta- 
tions charged  at  high  voltage,  may,  in  virtue  of  steadying 
the  load  prove  more  serviceable  than  rotary  converter  sta- 
tions. Their  use,  however,  is  certainly  of  special,  not  of 


SUBSTATIONS.  133 

general,  applicability  and  while  sometimes  convenient  as  a 
makeshift  or  as  the  simplest  solution  of  a  special  problem, 
they  should  be  employed  very  cautiously  in  the  present 
state  of  our  experience.  It  is  now  not  uncommon  to  use 
batteries  purely  for  the  purpose  of  steadying  the  load  and 
thus  improving  the  load  factor,  and  while  few  such  plants 
have  been  in  operation  long  enough  and  under  exact 
enough  conditions  to  determine  accurately  the  net  results, 
the  practice  is  worthy  of  more  than  a  passing  mention.  The 
logic  of  the  process  is  to  connect  a  battery  in  parallel  with 
the  generator,  charging  at  times  of  low  load  and  discharg- 
ing at  times  of  high  load.  The  beneficial  result  is  two- 
fold ;  the  generator  is  enabled  to  work  at  a  nearly  uniform 
load  well  up  toward  its  full  capacity,  and  hence  at  high 
economy  ;  and  by  this  reduction  in  load  fluctuations  it 
becomes  possible  to  use  a  smaller  generating  outfit  than 
would  otherwise  be  the  case.  The  price  paid  for  these  ad- 
vantages is  the  use  of  the  battery,  high  in  first  cost,  hav- 
ing a  rather  stiff  depreciation,  and  not  of  high  efficiency. 

To  form  a  clear  idea  of  the  conditions  which  exist  we 
may  refer  to  Fig.  7 1  which  is  taken  from  a  plant  in  regular 
operation  and  shows  the  total  output,  battery  output  and 
generator  output,  for  a  brief  typical  period.  In  the  first 
place  it  should  be  noted  that  the  battery  does  actually  take 
care  of  most  of  the  fluctuations,  reducing  the  generator  load 
to  a  fairly  steady  quantity.  An  inspection  of  the  generator 
curves  shows  that  a  50  k.  w.  machine  could  have  done  the 
work  perfectly  well  and  that  it  would  have  "worked  at  a 
load  factor  of  nearly  90  per  cent.  Unaided  by  the  battery 
a  machine  of  nearly  100  k.  w.  would  have  been  required, 
working  at  little  better  than  50  per  cent  load  factor.  Still 
greater  fluctuations  might  be  reasonably  expected,  but  it 
is  probably  not  far  from  the  truth  to  say  that  by  combining 
generator  and  battery  in  a  case  like  this  the  generator  need 
not  have  a  capacity  of  over  60  per  cent  the  normal  plant 
capacity.  The  plant  with  generator  alone  would  work  on 
the  average  at  rather  less  than  half  its  rated  capacity  while 
the  plant  with  battery  would  work  its  generator  at  nearly 


134    POWER   DISTRIBUTION    FOR   ELECTRIC   RAILROADS. 

80  per  cent  load  and  the  battery  would  stand  the  rest.  The 
battery  would  then  be  normally  perhaps  40  per  cent  of  the 
plant  with  a  power  of  doubling  its  discharge  rate  when 
necessary.  Now  let  us  see  to  what  this  leads.  Roughly 
the  cost  of  the  two  plants  would  be  about  the  same,  for  the 
cost  of  battery  would  more  than  offset  the  extra  capacity 
of  generator  boiler  and  engine  required  to  displace  it.  The 
general  effect  is  to  raise  the  load  factor  fully  30  per  cent. 
The  effect  of  this  on  the  economy  of  the  system  is  great,  as 


FIG.  71. 


appears  from  Fig.  64.  It  is  extremely  difficult  to  predi- 
cate the  cost  of  power  in  such  small  units,  but  it  is  per- 
fectly safe  to  say  that  the  smaller  plant  being  worked  at 
higher  efficiency  would  produce  i  k.  w.  h.  at  not  over  two- 
thirds  the  cost  in  the  larger  plant.  Of  course  it  has  to 
produce  more  power  since  each  k.  w.  delivered  through  the 
battery  means  at  least  1.25  k.  w.  delivered  to  the  battery, 
and  probably  rather  more  if  the  battery  takes  most  of  the 
fluctuations.  I^et  us  assume  that  the  smaller  generating 


SUBSTATIONS.  1 35 

plant  can  deliver  energy  at  4  cts.  per  k.  w.  h.,  and  the 
larger  one  at  6  cts.  per  k.  w.  h. ,  the  total  energy  required 
being  500  k.  w.  h.  per  day  on  the  line.  From  the  larger 
generating  plant  the  cost  of  power  would  be  $30  per  day. 
The  battery  plant  would  furnish,  say,  250  k.  w.  h.  direct, 
costing  $10  and  250  through  the  battery.  Allowing  this  a 
net  efficiency  of  75  per  cent,  it  would  require  333  k.  w.  h. 
which  at  4  cts.  amounts  to  $13.32.  Hence  the  battery 
plant  would  save  in  the  gross  cost  $6.68  per  day  or  annu- 
ally 10  per  cent  on  nearly  $25,000 — evidently  a  handsome 
saving.  Where  so  great  a  change  can  be  made  in  the  load 
factor  of  a  small  plant,  a  battery  rfcis  well  worth  using  in 
spite  of  extra  cost  and  care.  As  the  plant  increases  in  size 
a  point  is  reached  at  which  the  cost  of  and  loss  of  efficiency 
in  the  battery,  offsets  the  saving  from  improved  load  factor. 
Just  where  this  point  is,  is  hard  to  say,  but  if  the  load 
factor  of  a  plant  is  40  per  cent  or  less,  the  battery  question 
is  worth  raising  and  investigating  carefully.  In  case  a 
considerable  saving  is  probable  one  may  be  justified  in  put- 
ting the  battery  at  some  distance  from  the  generating 
plant  thus  getting  the  advantage  of  a  substation  to  offset 
the  extra  attendance  and  loss  in  charging,  and  if  the  load 
is  light  and  badly  scattered,  the  logical  outgrowth  of  the 
situation  may  be  several  battery  substations.  The  essence 
of  the  matter  is  the  possible  improvement  in  load  factor. 

•  The  whole  matter  can  perhaps  best  be  discussed  by 
taking  up  a  concrete  case  and  treating  it  first  by  the  ordi- 
nary methods  of  distribution,  and  second,  by  a  transmission 
system. 

We  will  assume  an  interurban  line  twenty  miles  long, 
A  B,  Fig.  70.  The  suburban  sections,  A  C  and  B  E,  each  re- 
quires an  actual  average  output  of  200  k.w.  which  may 
practically  all  be  concentrated  in  A  and  B  on  occasion. 
The  interurban  portions,  C  D  and  D  E,  require  together  an 
average  of  100  k.w.  nearly  uniformly  distributed.  What 
is  the  best  arrangement  for  supplying  power;  stations  at 
A  and  B,  stations  at  C  and  E,  a  single  station  at  D  or 


136    POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

transmission  of  all  the  power  from  some  one  point  with  sub- 
stations at  one  or  more  of  the  others? 

Of  the  plans  with  two  generating  stations,  that  with 
stations  at  A  and  B  is  undoubtedly  the  better  since  the  ter- 
minal loads  are  so  considerable.  The  single  station  at  D 
requires  a  little  consideration,  because  the  difference  in 
cost  of  power  between  a  500  k.w.  station  and  two  250  k.w. 
stations  is  very  material.  Of  the  possible  transmission 
plants,  that  comprising  a  generating  plant  at  one  end  of 
the  line  and  a  substation  at  or  near  the  other  is  at  first 
glance  the  most  promising.  For  the  total  amount  of  power 
to  be  transmitted  is  very  moderate  and  the  subdivision  of 
even  this  by  using  two  or  more  substations  would  only 
involve  useless  expense. 

We  may  now  compare  more  closely  the  plan  calling 
for  stations  at  A  and  B  with  that  for  the  installation  of  a 
single  plant  at  the  point  D.  On  the  one  hand  we  have  the 
economy  of  the  larger  station — on  the  other  the  cost  of 
distributing  200  k.w.  at  a  point  ten  miles  from  home. 

A 1 1 -4 -B 

C  ••  D 

FIG.  72. 

Assuming  the  yearly  differences  in  cost  of  power  be- 
tween a  500  k.  w.  station  and  two  250  k.  w.  stations  to  be 
about  $0.4  per  kilowatt  hour  in  favor  of  the  former,  the 
yearly  difference  is  $14,600.  Now  for  the  approximate  cost 
of  feeder  copper.  If  a  simple  station  at  D  be  used  we  must 
practically  allow  for  400  k.  w.  delivered  at  a  distance  of  ten 
miles.  Using  the  formula  employed  in  the  previous  cases 


E 

and  assuming  ten  per  cent  drop  we  have  a  call  for  940  tons 
of  feeder  copper  costing  about  $263,000.  Even  at  twenty 
per  cent  loss  the  feeder  copper  would  amount  to  more  than 
$130,000,  exclusive  of  the  nearer  distribution.  This  settles 
the  matter  off  hanfl,  for  with  two  stations  the  average  dis- 
tance of  transmission  would  be  hardly  more  than  three  to 


SUBSTATIONS.  137 

four  miles,  and  the  total  amount  of  feeder  copper  relatively 
Very  small.  In  a  less  extreme  case  a  closer  calculation  of 
feed  copper  would  be  required,  and  the  matter  could  be 
examined  with  any  necessary  degree  of  precision. 

With  two  generating  stations  we  may  as  a  first  ap- 
proximation assume  that  on  the  whole  400  k.  w.  is  trans- 
mitted an  average  distance  of  2}^  miles,  say,  14,000  ft., 
and  100  k.  w. ,  a  distance  of,  say,  40,000  ft.  For  the  first  item, 
there  would  be  necessary  about  sixty-six  tons  of  copper 
and  for  the  second  about  134  tons,  in  all  about  200  tons, 
costing,  say,  $56,000. 

Now  if  the  power  is  transmitted  from  A  to  B  we  shall 
have  a  saving  as  before  of  $14,600  in  the  gross  cost  of  gen- 
erating power,  but  lose  about  ten  per  cent  in  final  efficiency 
since  the  net  efficiency  of  line  and  apparatus  will  be 
roughly  eighty  per  cent  as  against  ninety  per  cent  for  the 
loss  in  feeders  as  above.  For  a  10,000  volt  transmission 
about  twenty  tons  of  copper  will  be  required  costing,  say, 
$5600.  The  transformers  and  rotary  converters  with  the 
requisite  accessory  apparatus  may  be  lumped  together  at 
about  $50  per  kilowatt  capacity.  Allowing  400  k.  w.  capacity 
at  the  substation  the  cost  of  transmission  line  and  appar- 
atus would  be  between  $25,000  and  $30,000.  Assuming 
the  latter  and  charging  off  ten  per  cent  for  interest  and  de- 
preciation we  have  a  fixed  charge  of  $3000  against  the 
plant.  Allowing  four  men  at  $75  a  month  each  at  the 
substation  and  five  per  cent  extra  on  the  plant  for  main- 
tenance of  line  and  repairs  we  have  a  total  charge  against 
the  transmission  of  $3000  -f-  $3600  -j-  $1500  +  I0  percent  of 
the  yearly  energy  which  at  1.3  cts.  per  kilowatt  hour  would 
.cost  about  $4745,  in  all  about  $12,845,  showing  a  small 
saving  in  favor  of  the  transmission  of  power.  The  differ- 
ence, however,  is  so  small  that  it  could  easily  be  thrown  on 
the  other  side  of  the  balance  sheet  by  a  slight  change  in 
local  conditions,  or  on  the  other  hand  it  might  chance  to  be 
increased.  The  exact  state  of  the  case  would  have  to  be 
determined  by  a  thorough  examination  of  the  change  of 
cost  of  power  with  size  of  station  in  the  localities  in  ques- 


138     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

tion.  It  goes  without  saying  that  the  curves  given  in  Fig. 
64,  while  closely  figured  for  the  assumed  conditions  are 
subject  to  too  much  variation  to  be  safely  applicable  to  the 
decision  of  a  close  case.  For  preliminary  investigation 
however  they  will  be  found  convenient. 

At  shorter  distances  than  that  just  assumed  the  same 
apparatus  would  generally  be  required  and  the  cost  of  line 
would  gradually  decrease,  but  so  slowly  that  the  economics 
of  the  case  would  remain  nearly  the  same.  The  minimum 
cost  for  the  case  considered  would  probably  be  given  by 
a  main  generating  station  at  some  convenient  point  be- 
tween A  and  C,  and  a  substation  about  midway  between  K 
and  B.  So  long  as  substation  apparatus  requires  the  same 
attention  as  generating  apparatus,  the  usefulness  of  power 
transmission  is  limited  to  a  comparatively  small  field.  If, 
however,  alternating  current  motors  come  into  regular  use 
so  that  the  only  substations  required  shall  be  static  trans- 
formers distributed  along  the  line,  the  use  of  more  than 
one  generating  station,  save  in  roads  on  a  large  scale,  will 
be  needless  and  wasteful.  A  very  important  problem 
which  has  of  late  assumed  great  importance  is  the  distribu- 
tion of  power  by  high  voltage  currents  not  to  scattered  sta- 
tions along  a  line,  but  from  a  huge  central  power  station  to 
its  auxiliaries.  It  is  power  transmission  versus  auxiliary 
stations  with  prime  movers — a  question  deserving  close  con- 
sideration by  itself.  For  example,  is  it  cheaper  to  generate 
power  separately  in  such  a  case  as  is  shown  in  Fig.  6 1 ,  or 
to  generate,  say  at  A,  and  transmit  to  the  other  stations? 
In  the  matter  as  thus  stated,  the  general  network  for  dis- 
tribution is  exactly  the  same  in  each  case  and  the  economic 
dilemma  is  an  immense  central  station  plus  transmission 
substations  versus  auxiliary  stations.  For  simplicity  let  us 
assume  as  the  units  to  be  compared  a  15,000  k.  w.  station 
with  five  2500  k.  w.  substations  with  rotary  converters, 
and  six  separate  2500  k.  w.  stations. 

The  fundamental  problem  is  the  relative  cost  of  power 
in  a  15,000  and  a  2500  k.  w.  station,  each  being  equipped 
in  the  best  modern  style,  and  the  costs  in  each  case  being 


SUBSTATIONS.  139 

carried  out  to  the  bitter  end,  including  the  interest  charges 
due  to  first  cost,  so  as  to  put  the  final  charge  per  kilowatt 
hour  on  an  absolutely  even  basis.  No  practical  data  on  a 
15,000  k.  w.  station  are  available,  but  Dr.  C.  E.  Emery 
has  made  a  most  thorough  and  keen  analysis  of  the  final 
cost  of  steam  power  in  a  20,000  B.  H.  P.  station.  For 
simplicity  we  will  assume  the  load  factor  of  63.8  per  cent 
which  is  taken  in  his  estimate,  since  as  a  matter  of  prac- 
tice this  figure  is  quite  nearly  that  regularly  reached  on  the 
Boston  and  Brooklyn  systems,  having  similar  or  greater 
output. 

On  the  basis  of  a  maximum  output  of  20,000  h.  p. 
every  day  in  the  year,  at  tj^ie  above  mean  load  factor,  and 
running  twenty-four  hours  per  day,  the  cost  per  brake 
horse  power  hour  is  estimated  by  Dr.  Emery  to  be,  coal 
being  $2.24  per  long  ton, 

0.378  cent 

Taking  this  figure  for  the  B.  H.  P.  at  the  dynamo  shaft  it 
is  not  difficult  to  make  the  necessary  corrections  for  the 
cost  and  labor  connected  with  the  electrical  part  of  the 
plant  and  to  reduce  the  result  to  cost  per  kilowatt  hour. 
At  present  prices  for  material  and  labor  the  net  result 
would  be 

0.62  cent  per  k.  w.  h. 

This  figure  is  notably  higher  than  some  of  the  published 
costs  of  power  in  existing  railway  plants  of  much  less  size, 
but  such  costs  generally  do  not  take  account  of  interest 
and  depreciation,  which  makes  a  very  material  difference. 
Data  from  existing  stations  of  2000-3000  k.  w.  capacity 
do  show,  however,  that  power  can  be  produced  in  them  at 
from,  say,  0.75  to 0.80  cent  per  k.  w.  h.,  with  all  expenses 
included.  In  the  present  state  of  knowledge  on  the  sub- 
ject one  may  fairly  say  that  in  passing  from  a  capacity  of 
2500  k.  w.  to  15,000  k.  w.  it  would  be  imprudent  to  reckon 
upon  a  saving  exceeding  20  per  cent.  Appearances  indi- 
cate a  saving  even  less  than  this,  if  we  may  judge  from  the 
saving  over  still  smaller  units. 

Now  bearing  in  mind  that  these  costs  have  already 


OK   THE 

UNIVERSITY 
&/? 


140     POWER   DISTRIBUTION    FOR   ELECTRIC    RAILROADS. 

taken  into  account  the  difference  in  cost  of  erection  be- 
tween one  very  large  plant  and  six  large  ones,  together  with 
all  similar  factors,  we  can  take  up  the  merits  of  transmis- 
sion at  high  voltage  to  rotary  converter  stations.  To  take 
the  most  favorable  case  we  will  assume  that  the  central 
station  furnishes  2500  k.  w.  directly  to  the  lines  and  is 
equipped  with  high  voltage  generators,  5000  or  6000  volts, 
for  the  remaining  12,500  k.w.  To  obtain  the  net  cost  of 
power  we  must  take  account  of  five  rotary  converter  sta- 
tions with  reducing  transformers,  necessary  labor,  trans- 
mission lines,  and  also  the  necessary  losses  in  transmission. 
Fortunately  rotaries  are  capable  of  being  compactly 
stowed  so  that  the  real  estate  charges  are  not  exorbitant 
and  while  they  cannot  go  without  attention,  require  little 
extra  labor.  At  high  voltage  the  loss  in  the  lines  is  not 
large,  and  both  transformers  and  rotaries  are  efficient.  We 
will  assume  the  net  all  day  efficiency  of  the  combination 
of  line  transformers  and  rotaries  to  be  about  85  per  cent, 
which  is  as  high  as  the  facts  will  warrant,  and  an  average 
distance  of  transmission  of  15,000  feet.  We  will  also 
assume  that  including  all  apparatus,  building,  and  land, 
each  station  of  the  five  costs  $90,000  and  that  only  one 
attendant  is  on  duty  at  a  time  in  each  station.  On  this 
basis  after  making  the  necessary  corrections,  the  cost  per 
k.  w.  h.  delivered  from  the  rotaries  becomes 

0.83  cent 

and  the  total  net  cost  of  power  on  the  system  becomes  al- 
most exactly 

0.8  cent. 

It  therefore  appears  that  under  the  conditions  assumed 
the  chances  are  against  any  economy  of  operation,  for 
the  assumed  saving  ,of  20  per  cent  in  the  original  cost  per 
k.  w.  h.  in  the  central  station.  In  the  writer's  opinion  15 
per  cent  would  be  a  liberal  estimate,  and  this  means  that 
the  system  of  power  distributed  to.  rotaries  would  cost 
nearly  10  per  cent  more  per  k.  w.  h.  than  if  generated  in 
individual  stations.  In  the  absence  of  data  on  very  large 
stations  all  these  figures  have  an  element  of  uncertainty;  but 


SUBSTATIONS.  141 

it  is  well  within  the  truth  to  put  the  case  as  follows:  If 
there  be  any  gain  in  the  distribution  of  power  by  rotary 
converters  on  the  scale  just  indicated,  it  must  be  sought 
elsewhere  than  in  the  economy  secured  by  concentration 
of  steam  plant. 

Conditions  may  easily  arise,  however,  such  as  will 
make  such  a  distribution  desirable.  In  the  first  place 
there  may  be  one  particularly  site  for  a  power  station  by 
utilizing  which  enough  would  be  gained  to  more  than  off- 
set the  losses  incurred  in  transmission.  In  Dr.  Kmery's 
investigation  of  the  cost  of  power  in  a  20,000  h.  p.  station 
the  total  cost  is  subdivided  as  follows: 

Coal 37. 3  per  cent. 

Labor 11.3    " 

Supplies  and  repairs J7-4    "       " 

Interest,  taxes,  renewals,  etc.       .       34.0    "       " 
Assuming  this  for  the  steam  power  delivered  to  the  dyna- 
mos and  making  the  necessary  modifications  for  the  pres- 
ence of  the  electrical  plant,  the  distribution  of  the  total 
cost  in  the  latter  case  will  be  about  as  follows: 

Coal 32  per  cent. 

Labor 13    "       " 

Supplies  and  repairs   .     .     .     .18*'       " 
Interest,  taxes,  renewals,  etc.     .37    "       " 
These  proportions  will  vary  from  place  to  place  but  are 
not  far  enough  from  the  mark  to  lose  their  usefulness  for 
the  purpose  to  which  we  are  about  to  apply  them. 

A  change  in  cost  of  coal  due  to  difference  of  transpor- 
tation facilities  would  have  to  amount  to  something  like  1 5 
per  cent  of  the  price  to  give  a  reasonable  chance  of  offset- 
ting the  extra  transmission  costs.  Labor,  and  supplies 
and  repairs,  evidently  will  not  vary  appreciably  except 
for  the  cost  of  water,  while  of  the  rest  only  the  costs  of 
real  estate  and  foundations  give  a  chance  for  material 
variations.  Concurrent  advantages  with  respect  to  coal, 
water,  real  estate  and  foundations  in  favor  of  a  particular 
site  may  render  transmission  to  rotary  converter  stations 
decidedly  desirable,  but  it  is  to  these  factors,  rather  than 
to  general  considerations,  that  we  must  look  in  drawing 


142    POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

our  conclusions.  Save  in  rare  instances  no  single  item 
mentioned  is  likely  to  turn  the  scale. 

Two  further  factors  must  be  taken  account  of ;  first 
the  absolute  magnitude  of  the  plant,  and  second  the  num- 
ber of  substations  involved.  As  to  the  former  considera- 
tion, doubling  the  assumed  output  with  the  same  number 
of  substations  as  before  would  leave  so  small  gain  in  econ- 
omy by  concentration  as  to  require  an  extraordinary 
combination  of  favorable  conditions  to  give  even  a  prospect 
of  final  economy. 

At  half  the  total  output  first  assumed,  on  the  other 
hand,  the  costs  of  power  generated  in  one  station  and  trans- 
mitted to  five  others,  and  of  power  generated  in  six  stations 
would  be  so  nearly  equal  that  any  considerable  advantage 
in  favor  of  one  site  for  a  station  would  settle  the  matter. 

In  the  case  of  employing  only  two  or  three  stations, 
the  chance  for  economical  transmission  is  usually  very 
small  in  urban  work — the  interurban  situation  has  already 
been  discussed. 

If,  however,  advantage  can  be  taken  of  transmission 
to  rotary  converters  to  considerably  increase  the  number 
of  substations,  the  conditions  are  radically  altered.  As 
has  already  been  shown,  increasing  the  number  of  stations 
decreases  the  feeder  copper  enormously,  and  in  the  author's 
judgment  the  logical  way  to  work  transmission  to  rotary 
converters  is  to  carry  the  number  of  substations  beyond 
wrhat  would  be  desirable  if  substations  with  prime  movers 
were  to  be  installed.  In  this  way  a  very  considerable  ad- 
vantage can  be  gained  if  conditions  are  favorable.  The 
adverse  factors  are  first,  the  additional  labor  required  ; 
second,  the  absolute  density  of  the  traffic,  determining  the 
normal  output  in  any  given  part  of  the  system  ;  and  third, 
the  effect  of  wandering  of  the  load  on  the  maximum  out- 
put in  any  district.  As  regards  the  first  count  it  may  be 
well  to  note  that  wages  of  one  constant  attendant  will 
amount  to  10  per  cent  on  the  cost  of  about  fifty  tons  of 
feeder  copper,  hence  there  is  an  evident  limit  to  the  profit- 
able use  of  apparatus  requiring  attendance.  In  the  next 
^lace,  the  actual  output  regularly  demanded  in  any  one 


SUBSTATIONS.  143 

section  predetermines  to  a  considerable  extent  the  output 
which  must  be  available  nearby,  and  finally  the  wandering 
load  demands  heavy  output  at  particular  points  at  particu- 
lar times,  possibly  half  the  total  load  being  concentrated 
in  one  small  region  toward  6  P.  M.  Hence  one  must  some- 
times deal  with  large  units  whether  other  conditions  are 
favorable  or  not. 

In  large  urban  systems  the  whole  problem  gets  tre- 
mendously intricate  and  cannot  be  settled  on  general  prin- 
ciples. Enough  has  been  said  to  indicate  the  line  of  reas- 
oning to  be  followed  and  the  rest  must  depend  upon  local 
conditions  as  they  may  exist.  But  the  questions  to  be 
decided  are,  as  has  been  shown,  so  close  that  the  final 
solution  of  the  matter — and  the  best  solution — is  likely  to 
be  different  in  different  places.  In  most  instances  a  close 
study  of  the  details  should  lead  to  the  use  of  more  than 
one  generating  station,  re-enforced  by  substations  with 
rotaries  where  they  can  be  advantageously  used.  And 
one  such  substation  ought  be  pretty  near  the  centre  of 
the  load  produced  by  the  maximum  concentration  of  cars. 
The  transmission  method  is  a  very  valuable  one  when 
properly  applied,  but  it  has  economic  limitations  that 
should  be  kept  steadily  in  mind. 

Just  at  present  the  most  promising  method  of  operat- 
ing roads  of  moderate  length  seems  to  be  the  use  of  direct 
feeding  at  high  voltage,  by  boosting,  the  three- wire  system 
or  the  like.  When  the  length  reaches  fifteen  or  twenty 
miles,  the  choice  is  between  separate  generating  plants  and 
true  substations  with  the  advantage  of  the  latter  slowly  in- 
creasing with  the  distances  involved.  In  cases  where  the 
amount  of  power  involved  is  very  great,  as  in  large  urban 
plants  like  the  Boston  one  or  in  extensive  suburban  serv- 
ice such  as  is  likely  to  be  met  in  the  transformation  of 
steam  into  electric  service,  auxiliary  stations  are  most 
likely  to  give  the  minimum  cost  of  power,  since  the  size  of 
each  plant  can  be  so  considerable  that  further  increase  will 
decrease  the  cost  of  power  only  to  a  minute  degree.  The 
.greatest  future  gain  in  systems  of  moderate  size  is  to  be 
sought  in  the  possible  use  of  alternating  motors. 


CHAPTER  VI. 

TRANSMISSION  OF  POWER  FOR  SUBSTATIONS. 

The  transmission  of  power  for  railway  purposes  is  a 
comparatively  simple  matter  so  far  as  methods  are  con- 
cerned. Inasmuch  as  railway  dynamos  are  already 
worked  at  a  comparatively  high  voltage,  as  high,  in  fact, 
as  any  continuous  current  generators  of  large  output, 
there  is  little  reason  to  consider  continuous  current  methods 
for  transmitting  power.  Large  generators  of  this  class 
cannot  be  built  for  voltage  high  enough  above  that  already 
used  in  railway  practice  to  make  it  worth  while  to  trans- 
mit current  for  transformation  by  motor  generators.  Thus 
it  is  that  for  the  purpose  in  hand  one  need  only  be  con- 
cerned with  the  use  of  alternating  currents,  polyphase 
and  other,  and  the  transmission  of  power  at  high  voltages, 
from  2000  volts  up  to  10,000  volts  or  more. 

To  begin  at  the  beginning,  it  should  be  understood 
that  all  generators  from  their  constructional  features  are 
essentially  fitted  for  the  production  of  alternating  currents. 
When  continuous  current  is  desired  the  current  derived 
from  the  armature  windings  has  to  be  commutated  to  re- 
duce it  from  its  original  alternating  form  to  being  unidi- 
rectional. Take,  for  example,  a  simple  drum  winding  in- 
tended for  continuous  current,  such  as  is  shown  in  Fig.  72. 
Tracing  out  the  direction  of  the  currents  as  shown  by  the 
arrows  one  sees  immediately  that  the  two  halves  of  the 
armature  are  in  parallel  between  brush  and  brush.  When 
the  armature  has  turned  through  180  degs.  the  coils  that 
originally  were  under  the  -f-  brush  have  come  under  the  — 
brush  and  are  generating  E.  M.  F.  in  a  direction  opposite 
to  the  original  one.  All  coils  as  they  pass  under  a  given 
brush  are  delivering  current  in  the  same  direction,  but 


TRANSMISSION  OF   POWER   FOR   SUBSTATIONS.        145 

when  they  have  turned  180  degs.  the  current  direction  in 
them  is  reversed  and  they  are  properly  related  to  the  other 
brush. 

If,  now,  the  brushes  turned  with  the  "armature  they 
would  be  alternately  -\-  and  — ,  changing  sign  at  each  half 
revolution,  and  leads  permanently  connected  with  them 
would  deliver  alternating  current.  The  same  result  would 
evidently  follow  if  two  opposite  commutator  segments  were 


FIG.  72. 

permanently  connected  each  to  a  collecting  ring  on  the 
armature  shaft.  The  number  of  alternations  per  minute 
is  evidently  2  ny  where  n  is  the  number  of  revolutions  per 
minute.  In  a  four  pole  machine  the  E.  M.  F.  in  a  given 
coil  would  evidently  change  sign  every  90  degs. ,  in  a  six 
pole  machine  every  60  degs.  and  so  on,  so  that  in  a  multi- 
polar  generator  the  E.  M.  F.  in  a  given  coil  would  have 
P  n  alternations  per  minute,  where  P  is  the  number  of  poles. 
If  the  armature  of  Fig.  72  were  revolving  at  1500  r.  p.  m. 
and  were  fitted  with  collecting  rings  we  could  take  off 
from  them  an  alternating  current  of  3000  alternations  per 


146     POWER    DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 

minute.  It  is  often  preferable  to  define  this  frequency  in 
terms  of  cycles  per  second.  A  cycle  is  the  period  from  a 
given  K.  M.  F.  to  a  second  E.  M.  F.  in  the  same  direc- 
tion. If  Fig.  73  shows  a  single  alternation  of  current,  then 
Fig.  74  depicts  a  single  cycle.  To  reduce  alternations  per 
minute  to  cycles  per  second,  divide  by  120.  Thus  the  cur- 
rent delivered  by  the  armature  of  Fig.  72  connected  as  an 
alternator  would  be  of  twenty-five  cycles  (~)per  second. 
In  designing  alternating  generators  for  high  voltage  it  is 
desirable  to  have  all  the  armature  conductors  in  series,  so 
that  the  armature  winding  is  arranged  with  that  in  view. 
The  usual  procedure  *s  to  wind  alternate  armature  coils  in 


FIGS.  73  AND  74. 

opposite  directions  so  that  as  they  approach  or  recede  from 
each  successive  pair  of  poles  the  K.  M.  Fs.  will  be  in  the 
same  direction. 

Inasmuch  as  the  frequency  employed  in  power  trans- 
mission work  is  quite  often  as  high  as  60  ~  it  is  evi- 
dent that  either  the  speed  must  be  high  or  there  must  be  a 
considerable  number  of  poles.  The  result  of  arranging  a 
generator  to  meet  these  conditions  is  the  production  of  a 
highly  specialized  type  of  alternator  apparently  quite  dis- 
tinct from  ordinary  continuous  current  dynamos.  As  a 
matter  of  fact  most  of  the  latter  class  can  be  made  into 
fair  alternators  by  the  proper  connection  of  collecting 
rings,  as  already  shown,  but  very  few  alternators  could  be 
made  to  give  continuous  current  successfully  by  the  addi- 
tion of  a  commutator.  Fig.  75  shows  the  general  type 


TRANSMISSION   OF   POWER    FOR   SUBSTATIONS.         147 

toward  which  modern  alternators  tend.  It  is  a  60  k.  w. 
Westinghouse  generator  giving  a  frequency  of  60  ~  at  600 
r.  p.  m.  This  size  is  wound  on  occasion  for  voltage  as  high 
as  5000.  The  armature  coils,  one  per  pole,  are  machine 
wound  on  forms,  heavily  insulated  and  sprung  into  slots  in 
the  armature  core.  This  simple  type  of  generator  has  been 
in  use  for  several  years  past  in  connection  with  a  10,000  volt 
line  from  raising  transformers,  for  sending  current  twenty- 
eight  miles  from  San  Antonio  Canyon  to  San  Bernardino, 
Cal.  Like  all  other  generators,  the  alternator  is  re- 
versible and  can  be  used  as  a  motor.  In  this  function, 
however,  it  possesses  some  curious  and  interesting  proper- 
ties which  will  be  discussed  later. 

The  most  characteristic  property  of  alternating  current 
is  its  potency  in  producing  inductive  action.  Such  action 
depends  on  changes  of  magnetic  field,  which  in  turn 
depend  on  variation  of  the  magnetizing  current,  and  an 
alternating  current  is  in  rapid  and  continuous  variation  all 
the  time. 

It  is  this  property  which  gives  alternating  current  its 
immense  advantages  in  power  transmission,  since  it  enables 
changes  of  voltage  to  be  made  very  simply  and  with  very 
trifling  loss  of  energy,  and  changes  of  voltage  are  abso- 
lutely essential  to  economical  transmission  over  long  dis- 
tances. 

From  our  original  formulae  for  figuring  wiring  it  at 
once  appears  that  for  a  given  percentage  of  energy  lost  in 
the  line,  the  area  of  copper  necessary  varies  inversely  as 
the  square  of  the  working  voltage.  For  doubling  the 
working  voltage  halves  the  current  corresponding  to  a  given 
amount  of  energy,  while  for  the  same  percentage  of  loss  it 
doubles  K,  which  appears  in  the  denominator  of  the  form- 
ulae. The  value  of  even  a  small  increase  of  working  volt- 
age appears  in  the  most  striking  manner  in  the  table  of 
Chap.  IV.  For  working  circuits  the  voltage  is  limited  to 
such  a  figure  as  permits  of  thoroughly  successful  insula- 
tion of  the  motors  under  service  conditions.  In  the  trans- 
mission the  limit  is  imposed  only  by  the  conditions  of  safe 


148    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

insulation  of  the  line  and  the  generator  or  transformers,, 
which  is  a  very  different  matter. 

Hence  while  for  railway  motor  service  most  of  the 
work  has  been  at  about  500  volts,  and  1000  volts  appears. 
to  be  the  extreme  limit  in  the  present  state  of  the  art,  al- 
ternating power  transmission  lines  are  very  generally 
worked  at  from  4000  or  5000  volts  up  to  10,000  or  much 
more.  The  transmission  of  power  to  the  Oerlikon  works 
near  Zurich,  Switzerland,  has  been  steadily  operated  for 
several  years  at  about  14,000  volts  on  the  line,  while  those 
at  San  Bernardino,  Sacramento,  and  Fresno,  Cal.,  are 
operated  at  from  10,000  to  1 1,000  volts.  This  means  that 
the  line  copper  required  is  less  than  one  per  cent  of  that 
which  would  be  needed  for  direct  feeding  of  the  motors  at 
the  same  percentage  of  loss.  For  railway  work  in  distrib- 
uting power  to  substations  nothing  less  than  5000  volts  is 
likely  to  be  used  and  10,000  will  be  frequent.  At  dis- 
tances at  which  substation  working  becomes  economical 
less  than  5000  volts  will  hardly  pay.  We  have  already 
seen  in  the  preceding  chapter  that  on  anything  less  than  a 
fifteen  or  twenty  mile  road,  transmission  to  sub-stations  is 
not  likely  to  compete  advantageously  with  the  ordinary 
device  of  separate  stations.  At  such  distances  10,000  volts 
is  to  be  recommended  as  a  standard  pressure. 

The  problem  of  getting  such  voltages  is  not  altogether 
simple.  The  most  usual  method  is  to  generate  the  power 
at  a  rather  moderate  voltage,  say,  500  or  1000,  and  then  to 
obtain  the  high  line  pressure  from  raising  transformers. 
For  voltages  of  10,000  and  upwards  this  is  by  far  the  best 
plan,  and  so  indeed  it  is  generally  for  5000  volts,  but  for 
pressures  up  to  the  last  mentioned  figure  and  even  above  it, 
there  is  a  strong  tendency  to  construct  special  high  volt- 
age dynamos  feeding  directly  into  the  line.  This  avoids 
the  cost  of  the  raising  transformers  and  the  loss  of  energy 
incurred  in  them.  On  the  other  hand  such  high  voltage 
dynamos  are  rather  difficult  and  expensive  to  construct 
and  somewhat  more  liable  to  deterioration  than  those  of 
lower  voltage.  While  it  is  possible  to  wind  alternators  in 


TRANSMISSION   OF   POWKR   FOR   SUBSTATIONS.         149 

the  ordinary  manner  for  pressures  of  5000  volts  or  so,  the 
thorough  insulation  of  the  moving  armature  becomes  a  very 
difficult  matter. 

Under  these  circumstances  it  is  far  better  to  design  the 
generator  in  such  wise  that  the  high  voltage  armature 
wires  shall  be  stationary,  and  the  field  magnet  then  be- 
comes the  moving  part  of  the  machine. 


FIG.  75. 

The  commonest  wray  of  arranging  such  a  generator  is 
to  place  the  armature  coils  in  slots  cut  in  the  inner  face  of  a 
laminated  iron  ring  and  to  revolve  within  this  ring  a  star 
shaped  multipolar  magnet,  occupying  the  position  of  the 
armature  in  Fig.  75.  Such  a  generator  is  shown  in  Fig. 
76.  The  proper  insulation  of  the  armature  coils  is  here  com- 
paratively easy  and  the  chance  of  their  breaking  down  is  very 
much  reduced.  It  should  be  remembered  that  5000  volts 
will  actually  spark  across  an  air  space  of  about  ^  in., 


I5O    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

and  the  power  of  such  a  pressure  to  break  down  insulation 
is  most  formidable.  If  in  addition  to  so  great  an  electric 
strain  the  armature  insulation  has  to  stand  prolonged 
vibration  and  centrifugal  strain  its  life  is  likely  to  be  some- 
what uncertain.  For  these  high  voltages  therefore  a  ma- 
chine  with  a  stationary  armature  is  much  to  be  preferred 
to  the  ordinary  types,  especially  since  the  latter  have  no 
compensating  advantages. 


Fig.  76. 

Another  and  a  very  ingenious  form  of  generator  with 
two  phase  stationary  armature  is  shown  in  Fig.  77.  Here 
the  armature  is  composed  of  two  laminated  rings  placed 
side  by  side  in  a  common  frame  a  short  distance  apart. 
Each  is  slotted  to  receive  heavily  insulated  rectangular 
coils  as  shown  in  Fig.  78.  The  revolving  part  of  this 
machine,  is  simply  a  steel  casting  furnished  with  a  set 
of  outwardly  projecting  laminated  pole  pieces  at  each 
end.  The  field  winding  is  a  single  fixed  circular  coil 
around  the  field  between  the  two  armature  rings.  The 
armature  current  is  taken  off  from  fixed  binding  posts 


TRANSMISSION   OF   POWER    FOR   SUBSTATIONS.         151 

instead  of  brushes,  just  as  in  the  generator  shown  in  Fig. 
76,  but  in  this  latter  machine  there  are  not  even  brushes 
for  the  field  current  or  any  other  purpose.  These  inductor 
dynamos  may  be  safely  wound  for  as  high  as  5000  volts 
even  in  machines  of  moderate  size. 

With  5000  volts  available  at  the  terminals  the  trans- 
mission of  power  over  moderate  distances  can  be  effected 


FIG.  77. 

more  cheaply  than  by  the  use  of  higher  voltages  derived 
from  raising  transformers.  The  economics  of  the  ques- 
tion involve  no  difficulties.  The  ccst  of  raising  trans- 
formers and  their  accessories  in  ordinarily  large  units  may 
be  taken  as  on  the  average  about  $10  per  kilowatt  of  out- 
put. At  1 0,000  volts,  the  pressure  generally  used  when 
raising  transformers  are  employed,  the  cost  of  copper  is  but 
one-fourth  that  required  for  transmission  at  5000  volts 
and  the  same  loss.  The  lattci  ^as  the  advantage  of  greater 


152     POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

efficiency  by  the  loss  in  the  raising  transformers,  say,  two 
per  cent,  and  the  depreciation  of  the  line  copper  is  less 
than  that  of  the  transformers.  On  the  other  hand  the  de- 
preciation in  the  high  voltage  generators  is  somewhat 
greater  than  in  the  low  voltage  ones.  Setting  these  re- 
spective qualities  off  against  each  other  we  can  say  for  an 
approximation  that  the  cost  of  transmission  becomes  equal 


FIG.  78. 

by  the  two  methods  when  three-fourths  of  the  cost  of 
copper  for  transmission  at  5000  volts  amounts  to  $10  per 
kilowatt  delivered.  The  distance  usually  corresponding  to 
this  condition  is  ten  or  twelve  miles.  In  sizes  from  250 
k.  w.  up,  stationary  armature  machines  are  now  built  for 
as  high  as  10,000  to  12,000  volts.  They  are  reliable,  cost 
considerably  less  than  low  voltage  machines  with  trans- 
formers, and  are  equally  or  more  efficient.  Where  10,000 
or  12,000  volts  is  sufficient  they  give  admirable  results  and 
are  coming  into  extensive  use. 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS.          153 

One  cannot  well  theorize  on  this  matter,  however, 
since  the  prices  of  copper  and  apparatus  are  subject  to 
frequent  variations  and  in  actually  making  contracts  these 
variations  are  very  arbitrary  in  character.  It  is  some- 
times for  the  interest  of  a  bidder  to  cut  prices  on  some 
particular  arrangement  of  apparatus  or  to  raise  them  on 
another,  quite  overturning  the  buyer's  preconceived 
notions  on  the  subject. 

The  transformers  used  in  this  heavy  transmission  work 
are  very  different  in  appearance  from  the  familiar  little 
ones  that  decorate  the  poles  of 
electric  lighting  companies,  al- 
though, of  course,  identical  in 
principle. 

The  output  of  an  alternating 
current  transformer,  the  general 
features  of  the  design  remaining 
the  same,  would  naturally,  save 
for  the  question  of  heating,  in- 
crease rather  faster  than  in  pro- 
portion to  its  aggregate  weight  of 
copper  and  iron.  But,  other 
things  being  equal,  the  weight 

increases  as  the  cube  of  the  linear  dimensions,  while  the 
surface  increases  only  as  their  square.  Hence  the  heat  into 
which  the  energy  losses  in  a  transformer  are  converted  has 
less  chance  to  escape  by  radiation  in  a  large  than  in  a 
small  transformer,  the  available  surface  area  per  watt  being 
much  reduced.  Therefore  unless  there  are  special  precau- 
tions taken  the  large  sizes  will  run  too  hot  and  endanger 
the  insulation. 

So  the  ordinary  small  transformer,  of  which  the  core 
and  coils  are  shown  in  Fig.  79,  cannot  be  indefinitely  in- 
creased in  size  without  taking  care  to  provide  means  for 
compensating  the  lack  of  proper  radiating  surface  for  get- 
ting rid  of  the  heat. 

There  are  several  methods  of  doing  this.  One  of  the 
best  is  by  filling  the  transformer  case  with  oil.  This  by  its 


154  POWER   DISTRIBUTION   FOR    ELECTRIC   RAILROADS. 

mere  presence  in  the  case  assists  in  transferring  the  heat 
from  the  core  and  coils  to  the  case  whence  it  can  be  radi- 
ated, and  may  increase  the  possible  output  for  the  same 
heating  by  ten  per  cent  or  more.  In  large  transformers  it 
is  usual  to  go  further  and  to  cool  the  oil  artificially  either 
by  a  worm  through  which  cold  water  is  kept  circulating  or 
by  circulating  the  oil  itself  through  a  cooling  worm. 

An  excellent  example  of  the  former  practice  is  shown 
in  Fig.  80,  which  is  a  100  k.  w.  Westinghouse  substation 


FIG.  80. 

transformer  taken  apart  to  show  the  construction.  The 
case  is  an  iron  cylinder,  in  which  the  core  and  its  coils  are 
placed.  The  case  is  then  filled  with  paraffine  oil.  Just 
inside  the  case,  between  it  and  the  coils,  is  the  cooling 
worm  of  galvanized  iron  through  which  a  constant  stream 
of  cold  water  is  kept  flowing.  This  keeps  down  the 
temperature  so  that  a  large  output  can  be  obtained 
without  loss  of  efficiency.  For  the  efficiency  depends  on 
the  ratio  between  the  output  and  the  sum  of  the  losses 
in  the  core  and  the  coils.  The  losses  in  the  former 
are  nearly  constant,  so  that  if  they  form  a  considerable  por- 
tion of  the  total  loss  the  efficiency  may  even  increase  with 
increase  of  output. 

Another  equally  effective  method  of  obtaining  a  high 


TRANSMISSION  OF   POWER   FOR  SUBSTATIONS.         155 

output  without  overheating  is  by  building  the  transformer 
core  of  bunches  of  iron  laminae  separated  by  air  spaces  of 
j£  in.  to  YZ  in.,  subdividing  the  coils  in  a  similar  manner, 
and  then  forcing  through  the  whole  structure  a  stream  oi 
cool  air  from  a  small  blower.  This  construction  both  keeps 
the  transformer  cool  and  by  subdividing  the  primary  and 
secondary  coils  renders  it  easy  to  insulate  for  high  voltages. 


81. 


Fig.  8 1  shows  a  large  substation  transformer  made  in 
the  fashion  just  described,  stripped  of  its  connections  and 
external  casing  so  as  to  be  more  easily  seen.  The  coils  are 
wound  rather  deep  and  thin  and  the  primary  and  second- 
ary sections  alternate  with  heavy  insulation  between  each 
section.  The  cooling  blast  is  introduced  from  the  bottom. 
Channels  for  the  air  are  arranged  under  each  transformer 
and  a  small  motor  blower  furnishes  the  blast,  a  single 


156    POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

horse  power  being  ample  to  supply  the  air  for  cooling 
transformers  of  some  hundreds  of  kilowatts  capacity. 

Such  air  cooled  transformers  are  capable  of  giving  a 
large  output  for  their  weight  and  a  very  high  efficiency. 
The  average  weight  runs  about  twenty  to  twenty-five 
pounds  per  kilowatt  of  output,  while  the  efficiency  reaches 
and  sometimes  exceeds  ninety-eight  per  cent. 

There  is  no  difficulty  in  constructing  these  large  sub- 
station transformers  to  give  10,000  volts  or  more  from  the 
high  voltage  coil  and  their  construction  is  such  that  they 
are  little  subject  to  accident.  The  air  blast  transformers 
separate  the  primary  and  secondary  coils  by  air  spaces  and 
heavy  mica  insulation,  while  those  in  which  oil  is  employed 
add  its  very  high  insulating  properties  to  those  already  ob- 
tained from  the  construction  of  the  transformers.  Either 
type  is  thoroughly  reliable  for  substation  working.  These 
high  voltage  transformers  should  always  be  placed  in  a  room 
by  themselves,  out  of  reach  of  all  save  the  employes  whose 
regular  work  it  is  to  care  for  them,  for  5000  to  10,000  volts 
means  danger  and  should  be  treated  with  due  respect.  At 
such  voltages  no  ordinary  insulation  is  any  guarantee  of 
safety  and  bare  wire  which  bears  evidence  of  danger  on  its 
face  is  quite  as  desirable  as  any  insulated  wire. 

Perhaps  the  best  plan  for  taking  care  of  extreme  volt- 
ages in  generating  or  substations  is  to  isolate  them  and  keep 
them  out  of  reach  as  far  as  possible,  using  switchboards  with 
no  exposed  wiring  on  their  faces.  What  wiring  is  necessary 
should  be  on  porcelain  insulators,  not  crowded,  and  per- 
fectly accessible  when  occasion  demands,  but  not  other- 
wise. Particular  care  should  be  taken  to  have  the  course 
of  high  tension  wires  obvious  at  a  glance,  avoiding  all  in- 
volved connections,  so  that  it  will  be  possible  to  trace  at 
once  every  such  wire  from  its  origin  at  the  high  tension 
terminals  of  the  transformers  through  the  switchboard,  if 
there  be  one,  and  safely  out  of  the  building  to  the  line. 

Bear  in  mind  that  for  the  sake  of  simplicity,  economy 
and  efficiency,  the  transformer  units  should  be  few  in 
number  and  of  large  size  rather  than  many  and  of  moder- 


TRANSMISSION   OF   POWER    FOR  SUBSTATIONS.         157 

ate  size.  When,  however,  the  individual  transformers  can 
be  of  considerable  output,  say,  fifty  to  one  hundred  kilo- 
watts, further  increase  in  size  is  less  important,  for  beyond 
such  outputs  the  increase  in  efficiency  and  decrease  in 
relative  cost  is  much  slower  than  the  variation  in  smaller 
sizes.  The  increase  of  efficiency  in  passing,  for  instance, 
from  a  ten  kilowatt  transformer  to  one  of  one  hundred 
kilowatts  is  about  2  to  2  ^  per  cent,  while  in  passing  from  a 
one  hundred  kilowatt  transformer  to  one  of  500  to  1000 
k.  w.  the  increase  in  efficiency  is*  decidedly  less  than  one 
per  cent. 

With  respect  to  the  treatment  of  high  voltage  trans- 
mission wires  after  leaving  the  stations,  much  might  be 
said,  but  since  ordinary  precautions  for  high  voltage  are 
obvious  to  the  engineer  it  is  sufficient  to  emphasize  a  few 
points  dictated  by  experience. 

As  to  poles,  as  in  many  other  matters,  in  the  long  run 
the  best  is  the  cheapest.  Clean  selected  cedar  is  by  far  the 
best  material  available  in  this  country.  The  poles  for 
power  transmission  work  should  be  somewhat  longer  and 
stronger  than  usual,  for  they  have  to  carry  substantial 
wires,  often  through  open  country  where  the  wind  has 
full  sweep.  The  length  should  be  great  enough  to  keep 
the  wires  well  out  of  the  way  and  to  permit  carrying  the 
lines  easily  over  ordinary  circuits  when  crossing  is  abso- 
lutely necessary.  A  good  standard  is  a  forty  foot  pole 
with  a  seven  inch  top,  set  fully  six  feet  in  well  tamped 
earth.  Now  and  then  for  runs  across  clear  country  thirty- 
five  foot  poles  may  well  be  used,  but  the  tops  should  gener- 
ally be  seven  inches,  and  the  setting  about  five  feet  six 
inches  deep.  The  poles  should  run  not  less  than  about 
fifty  to  the  mile.  Such  a  line  may  appear  needlessly 
heavy,  but  inasmuch  as  continuity  of  service  depends  on 
the  integrity  of  the  line,  the  precautions  are  well  taken. 
For  the  same  reason  the  cross  arms  should  be  extra  strong 
and  secured  to  the  poles  with  special  care. 

The  matter  of  insulators  is  of  the  utmost  importance. 
Up  to  4000  or  5000  volts  large,  strong,  double  petticoat, 


158   POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

glass  insulators  will  give  good  results.  Such  insulators 
have  been  in  use  on  arc  circuits  of  similar  voltage  for  years 
with  uniform  success.  Glass  insulators  of  special  construc- 
tion with  extra  deep  petticoats  have  been  successfully  em- 
ployed with  even  10,000  volts  alternating.  A  pole  head 
equipped  with  such  insulators  is  shown  in  Fig.  82.  This 


FIG.  82. 

is  the  type  of  insulator  used  in  the  San  Antonio  Canyon 
plant,  to  which  reference  has  been  made. 

At  so  high  a  pressure,  however,  porcelain  is  much  to 
be  preferred,  owing  to  its  higher  insulating  properties,  par- 
ticularly after  protracted  weathering,  and  to  its  great 
mechanical  strength.  It  should  be  distinctly  understood 
that  poor  porcelain  is  worse  than  glass  and  that  to  be  effect- 
ive as  an  insulator  the  porcelain  must  have  not  merely  a 
surface  glaze,  but  must  be  strongly  vitrified  clear  through. 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS. 


159 


A  good  test  of  quality  is  to  chip  through  the  external  sur- 
face and  place  the  point  of  a  well  filled  pen  on  the  break. 
If  the  ink  flows  and  produces  a  spreading  stain,  and  partic- 
ularly if  it  works  under  the  exterior  glaze,  the  porcelain  is 
probably  worthless  as  an  insulator.  Much  cheap  porcelain 


One  third  sire 


FIG.   83. 

is  somewhat  hygroscopic  and  in  a  damp  climate  is  utterly 
worthless. 

First  class  porcelain,  however,  is  an  ideal  substance 
for  insulators  on  all  long,  high  voltage  lines.  For  this 
purpose  the  insulators  should  all  be  tested  and  should  not 
break  down  at  double  the  normal  voltage. 

An  excellent  specimen  of  these  high  grade  porcelain 
insulatiors  is  shown  in  Fig.  83.  This  particular  form  was 


POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 


developed  for  the  Niagara- Buffalo  transmission  line  in  which 
a  voltage  of  20,000  is  designed  to  be  used.  The  insulators 
were  tested  at  40,000  volts  and  very  few  had  to  be  rejected 
lor  failure.  They  depend  for  their  insulating  power  on  the 
quality  of  the  porcelain  and  on  well  designed  double  petti- 
coats. Such  insulators  are  admirably  adapted  for  work  up 

to  at  least  20,000  volts,  provided 
the  climate  is  reasonably  good. 
In  very  moist  climates  where  the 
insulators  are  exposed  to  f  requenJ 
searching  mists  and  nearly  con- 
stant dampness  still  further  pre- 
cautions are  desirable,  and  these 
excellent  results  can  be  secured 
by  using  oil  insulators  of  which  a 
very  good  specimen  is  shown  in 
section  in  Fig.  84.  The  pin,  P,  of 
iron,  is  cemented  into  the  body  of 
the  insulator,  I,  which  is  made 
thick  and  solid.  The  thick  bell  of 
the  insulator  is  turned  inwards 
and  upwards  at  its  lower  edge  so 
as  to  form  a  circular  cup,  C.  This 
cup  is  filled  with  highly  insulating 
oil,  which  is  exceedingly  efficient 
in  stopping  leakage  along  the  surface  of  the  insulator  to  the 
iron  pin.  In  dry  and  dusty  weather,  however,  the  oil  accum- 
ulates dirt  and  is  likely  to  be  reduced  to  a  species  of  mud, 
quite  destroying  its  insulating  value.  The  oil  insulator 
seems  to  be  passing  out  of  use,  but  for  very  high  voltages 
in  damp  climates  it  has  merits. 

With  respect  to  the  general  arrangement  of  a  trans- 
mission line  too  much  care  can  hardly  be  taken  in  keeping 
the  circuit  away  from  danger  of  accidental  contact  to  per- 
sons and  things.  Bare  wire  is  preferable  to  insulated  since 
it  does  not  encourage  a  feeling  of  false  security,  and  it 
should  be  distinctly  understood  that  the  wires  are  danger- 
ous and  must  be  let  alone.  Particular  pains  should  be 


FIG.  84. 


TRANSMISSION  OF   POWER   FOR  SUBSTATIONS.         l6l 

taken  to  carry  the  wires  clear  of  other  circuits,  arranging 
guard  wires  for  their  mutual  protection  whenever  they  can 
do  good.  If  the  circuit  runs  through  a  wooded  region  the 
branches  of  trees  and  all  dead  wood  should  be  cleared  away 
so  that  nothing  can  sway  against  or  fall  upon  the  trans- 
mission wires.  The  wire  itself  should  be  jointed  when  nec- 
essary with  unusual  thoroughness,  and  should  be  inspected 
at  the  original  joints  if  such  there  are.  It  is  one  advan- 
tage of  bare  wire,  that  there  is  no  covering  to  hide  careless 
joints.  The  line  as  a  whole  should  be  easily  reached  for 
inspection  or  possible  repairs.  If  it  does  not  run  along 
the  track  it  should  follow  a  public  road  or  good  pathway 
so  that  any  point  can  be  quickly  reached  by  wagon  or 
bicycle. 

Up  to  this  point  we  have  been  dealing  with  principles 
common  to  all  alternating  transmission  systems  irrespec- 
tive of  particular  characteristics.  As  a  matter  of  fact  or- 
dinary single  phase  alternators  are  seldom  used  at  present 
for  transmission  purposes.  Although  the  single  phase 
alternator  is,  like  other  dynamos,  reversible  and  can  readily 
be  used  as  a  motor,  inability  to  start  as  a  motor  is  per- 
haps its  best  known  characteristic.  This  makes  it  singu- 
larly inconvenient  for  most  purposes,  and  while  the  diffi- 
culty can  be  overcome  by  using  induction  instead  of 
synchronous  motors,  single  phase  induction  motors  are 
not  satisfactory  for  large  powers  and  cause  a  heavy  induct- 
ance on  the  system  that  is  troublesome  in  more  ways  than 
one. 

For  railway  distribution  it  is  at  present  generally  nec- 
essary to  convert  the  transmitted  energy  at  the  substation 
into  the  form  of  continuous  current.  The  means  taken  to 
do  this  are  quite  various,  but  they  all  involve  the  starting 
oC  rotary  apparatus,  virtually  of  motors,  whatever  their 
function  may  be  ultimately.  So  the  problem  of  utilizing 
an  alternating  transmission  for  railway  purposes  begins 
with  the  task  of  starting  a  synchronous  alternating  motor. 
There  have  been  many  ingenious  plans  devised  for  this 
purpose,  some  of  them  depending  on  the  action  of  a  com- 


1 62     POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

mutator  during  the  period  of  getting  up  to  speed.  The 
only  device  practically  used  in  this  country,  however,  is 
the  rather  obvious  one  of  bringing  the  synchronous  motor 
up  to  speed  by  means  of  an  alternating  induction  motor, 
and  then  cutting  out  the  latter,  leaving  the  former  to  run 
in  synchronism  and  take  up  its  load  from  a  clutch. 

This  arrangement  while  perfectly  applicable  for  sub- 
station work  has  been  largely  superseded  for  all  purposes 
by  polyphase  motors,  which  start  easily  and  unassisted 
under  their  own  torque. 

The  general  principles  of  the  polyphase  systems  are 
at  the  present  time  sufficiently  well  known  to  engineers  to 
render  detailed  explanation  here  unnecessary.  By  poly- 
phase it  is  here  intended  to  designate  all  alternating  systems 
employing  two  or  more  alternating  currents  displaced  in 
phase  in  a  uniform  and  systematic  way.  Practically  there 
are  two  species  of  this  genus,  one  having  two  alternating 
currents  90  degs.  apart  in  phase,  the  other  having  three 
currents  120  degs.  apart  in  phase.  There  are  several 
varieties  of  each,  but  it  may  be  stated  broadly  that  for  the 
practical  purpose  of  transmitting  power  to  substations  for 
railway  purposes,  both  the  species  and  their  varieties  are 
substantially  equivalent.  From  an  academic  standpoint 
wide  differences  may  be  pointed  out,  and  in  certain  branches 
of  polyphase  work  the  differences  may  be  worth  consid- 
ering. The  three-phase  system  has  the  important  advant- 
age of  saving  25  per  cent  of  the  line  copper,  for  the  same 
maximum  voltage  between  wires.  But  as  a  two-phase 
current  is  very  easily  changed  into  a  three-phase  one  and 
back  again  in  the  raising  and  reducing  transformers,  the 
type  of  apparatus  used  makes  little  difference  in  the  net 
result.  Practically  this  change  is  nearly  always  made  on 
long  transmission  lines,  so  that  one  gains  the  advantage  of 
the  saving  in  copper,  whether  three-phase  or  two-phase 
machines  are  actually  used  in  the  stations.  So  far  as  the 
railway  engineer  is  concerned  these  differences  are  practi- 
cally negligible. 

Of  course,  polyphase  apparatus  is  closely  similar  to 
that  used  for  ordinary  single-phase  work  in  general  ar- 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS.          163 

rangement.  The  principal  differences  are  to  be  found  in 
the  armature  windings.  Two  phase  dynamos  and  motors 
customarily  have  two  separate  windings  on  the  armature, 
displaced  90  degs.  with  reference  to  their  spacing  be- 


FIG.  86. 

tween  consecutive  poles.  This  kind  of  winding  with  its 
overlapping  coils  is  admirably  shown  in  the  Stanley  two 
phase  machine  shown  in  Fig.  78.  Three  phase  generators 
are  similarly  arranged  except  that  there  are  three  sets  of 
coils  usually  spaced  60  degs.  apart,  one  set  being  reversed 


164  POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

to  give  the  requisite  120  deg.  phase  difference.  The 
windings,. are,  for  convenience  or  for  special  purposes,  var- 
iously modified  in  different  machines,  but  the  general  ar- 
rangements are  as  just  indicated. 

Polyphase  generators  as  a  class  give  a  rather  better 
output  for  their  weight  than  single  phase  machines,  owing 
to  a  better  utilization  of  the  armature  space  by  the  dis- 
tributed windings.  As  a  rule,  too,  they  represent  later 
and  better  ideas  in  design,  hence  are  apt  to  be  more  efficient 
and  to  regulate  better  than  ordinary  alternators.  Perhaps 
the  best  example  of  the  two  phase  type  is  to  be  found  in 
the  huge  5000  h.  p.  Niagara  generators,  one  of  which  is 
shown  in  Fig.  86  during  the  process  of  assembling,  with 
the  field  ring  ready  to  slip  into  place.  The  stationary 
armature  has  its  coils  set  in  deep  slots  in  the  laminations 
and  is  provided  with  ample  ventilating  ducts.  The  arma- 
ture winding  does  not  consist  simply  of  one  coil  per  phase 
per  pole  as  shown  in  Fig.  78,  but  each  phase  winding  con- 
sists of  a  number  of  coils  in  adjacent  slots,  thus  occupying 
the  armature  surface  to  better  advantage.  Such  a  con- 
struction is  very  often  employed  in  large  polyphase 
machines. 

The  revolving  field  is  here  external  to  the  armature, 
so  that  its  weight  gives  the  effect  of  a  gigantic  flywheel. 
The  commercial  efficiency  of  this  generator  at  full  load 
is  almost  exactly  ninety-seven  per  cent,  a  figure  due 
to  the  combination  of  careful  design  and  immense  size. 
These  Niagara  generators  are  probably  destined  to  play  a 
very  important  part  in  the  development  of  electric  railroads 
over  a  radius  of  many  miles. 

Machines  with  vertical  armature  shafts  are  rather  rare 
in  American  practice,  the  ordinary  horizontal  arrangement 
being  more  generally  convenient.  Hence  the  usual  type 
of  polyphase  generator  is  not  that  found  at  Niagara,  but  is 
more  nearly  akin  in  appearance  to  familiar  forms.  A  thor- 
oughly typical  example  of  recent  practice  in  three  phase 
generators  is  shown  in  Fig.  87.  This  exhibits  the  dynamo 
room  of  the  three  phase  transmission  plant  at  Folsom,  Cal., 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS. 


165 


containing  four  750  k.  w.  generators.  These  machines  run 
ac  300  r.  p.  m.  and  deliver  current  at  about  800  volts  and 


60  cycles  per  second.  The  armatures  are  built,  like  those 
of  the  Niagara  generators,  with  several  slots  per  phase  per 
pole,  so  that  the  armature  inductance  is  very  low  and  the 


1 66   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

variation  in  voltage  with  change  of  load  almost  negligible. 
The  machines  are  primarily  intended  for  direct  coupling, 
as  is  generally  the  case  with  dynamos  of  so  great  output, 
and  in  this  case  they  are  connected  to  double  horizontal 
turbines  working  under  a  head  of  about  fifty  feet.  Thf 
shafts  pass  through  close  fitting  sleeves  to  the  exterior  of 
the  power  house  where  the  turbines  are  located.  The 
transformers  of  the  air  ventilated  type  already  described 
are  located  above  the  dynamo  room  and  serve  to  raise  the 
line  pressure  to  nearly  11,000  volts  for  transmission  twenty- 
three  miles  to  Sacramento.  The  four  generators  are  oper- 
ated in  parallel,  as  is  the  case  with  most  plants  in  which 
modern  polyphase  apparatus  is  employed.  It  should  be 
noted  that  such  parallel  running  is  very  easy  if  the  gener- 
ators are  so  designed  that  they  have  good  inherent  regula- 
tion. The  commercial  efficiency  of  the  Folsom  machines 
is  about  ninety-six  per  cent  at  full  load. 

Generally  speaking  these  and  other  polyphase  ma- 
chines are  characterized  by  higher  efficiency,  lower  induct- 
ance and  enormously  better  regulation  than  is  to  be  found 
in  any  of  the  older  alternators.  The  value  of  the  two 
latter  characteristics  for  power  transmission  on  a  large 
scale  can  hardly  be  overestimated. 

The  efficiency  of  these  modern  generators  is  subject  to 
some  variation  according  to  size  and  speed,  but  between 
different  makes  of  the  same  size,  speed  and  voltage  the 
differences  are  small.  The  following  is  about  what  can  be 
counted  on  at  full  load  from  polyphase  generators  of  vari- 
ous sizes: 

Output  Efficiency 

in  k.  w.  per  cent. 

50—  ioo  92—93 

loo —  200  93 — 94 

200—  500  94—95 

500 — looo  95 — 96 

This  supposes  moderate  voltages,  say,  not  exceeding  4000 
in  the  larger  machines  or  2000  in  the  smaller.  It  also 
supposes  the  speeds  to  be  fairly  high — not  below  500  r.  p.  m. 
for  the  sizes  up  to  200  k.  w.,  and  not  below,  say,  200 


TRANSMISSION   OK   POWER   FOR   SUBSTATIONS.          167 

for  the  larger  sizes.  Slower  speeds  and  higher  voltages 
than  those  mentioned  are  very  likely  to  reduce  the  effi- 
ciency by  one  or  two  per  cent,  even  more  for  small 
sizes  running  at  unusually  low  speeds.  If  the  prime 
mover  is  of  low  speed,  such,  for  example,  as  a  Corliss  en- 
gine, it  is  quite  easy  to  lose  more  in  efficiency  by  using 
small  direct  coupled  generators  of,  say,  100  k.  w.  or  less, 
than  would  be  lost  by  belt  driving. 

Inasmuch  as  practically  all  railway  work  is  at  present 
done  by  continuous  current,  the  energy  received  at  any 
substation,  transmitted  by  alternating  current,  simple  or 
polyphase,  must  be  changed  into  continuous  current  for 
use  on  the  working  circuit.  There  are  various  ways  of 
effecting  this  transmutation,  all  of  them,  unfortunately, 
quite  inefficient  compared  with  the  results  obtained  from 
static  transformers,  and  what  is  worse,  all  requiring  atten- 
tion which,  however  slight,  cannot  be  dispensed  with. 

The  most  obvious  plan  is  to  employ  a  motor  driven  from 
the  alternating  circuit  by  belting  or  coupling  it  to  a  contin- 
uous current  dynamo.  Such  is  the  simplest  and  often  the 
cheapest  method  when  existing  stations  are  to  be  converted 
into  substations  operated  from  a  transmission  plant.  The 
engine  can  be  removed  or  merely  disconnected,  and  a 
synchronous  motor  installed  to  take  its  place  in  driving  the 
dynamos.  This  is  the  arrangement  which  has  been  used 
for  several  years  past  at  Hartford,  Conn.,  and  Taftville, 
Conn. ,  in  both  of  which  places  the  already  existing  gen- 
erators were  driven  from  polyphase  synchronous  motors. 
The  same  practice  is  followed  in  the  Folsom-Sacramento 
transmission.  At  the  latter  place  generators  for  the  elec- 
tric railway  and  for  other  purposes  are  driven  from  a  coun- 
tershaft which  receives  its  power  from  three  phase  syn- 
chronous motors.  The  generator  room  of  the  Sacramento 
substation,  which  is  a  typical  example  of  the  practice 
under  consideration,  is  shown  in  Fig.  88. 

Obtaining  continuous  current  in  this  way  is  often 
very  convenient,  but  is  most  reprehensible  from  the  stand- 
point of  efficiency.  It  may  answer  well  enough  for  the 


UNIVERSITY 


1 68   POWER   DISTRIBUTION  FOR   ELECTRIC   RAILROADS. 

utilization  of  very  cheap  water  power,  but  for  general  sub- 
station work  it  should  not  be  seriously  considered.     Allow- 


ing ninety-three  per  cent  efficiency  for  both  generator  and 
motor,  which  is  certainly  as  high  as  ordinarily  found  in 
practice,  and  taking  the  loss  in  belt  and  countershaft  as 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS.          169 

ten  per  cent  at  full  load,  which  is  low,  the  net  efficiency  of 
the  combination  from  the  energy  received  by  the  motor  to 
that  delivered  by  the  generator  is  only  seventy-eight  per 
cent.  This  loss  of  twenty-two  per  cent  of  the  total  energy 
in  changing  from  alternating  to  continuous  current  is  too 
considerable  to  be  endured  unless  under  very  exceptional 
circumstances. 

An  alternative  method  is  the  use  of  a  species  of  com- 
posite machine  composed  of  alternating  motor  and  contin- 
uous current  dynamo  assembled  on  the  same  base.  As  the 
two  elements  are  rigidly  in  line,  usually  have  one  common 
bearing  and  are  relieved  from  belt  strain,  their  combined 
efficiency  should  be  perhaps  a  couple  of  per  cent  better 
than  would  be  indicated  by  their  efficiencies  taken  separ- 
ately. Such  composite  machines  are  sometimes  used  in  this 
country,  and  not  infrequently  abroad,  chiefly  for  lighting 
work.  Fig.  89  shows  a  fine  500  k.  w.  motor  generator,  three- 
phase  to  continuous  current,  employed  on  the  great  80 
mile,  33,000  volt  transmission  to  Los  Angeles,  Cal.  In 
units  of  200  k.  w.  or  so,  such  machines  should  show  a  full 
load  efficiency  of  about  88  per  cent  if  properly  designed. 

Sometimes  windings  for  both  kinds  of  current  are  put 
on  a  single  armature  core,  but  this  device  has  little  to 
recommend  it. 

For  railway  work  by  far  the  best  method  of  obtaining 
continuous  from  polyphase  current  is  by  the  use  of  the  ap- 
paratus variously  known  as  rotary  transformer  or  rotary 
converter.  The  principle  of  this  machine  can  be  readily 
seen  by  reference  to  Fig.  72.  If  the  armature  here  shown 
is  put  in  rotation  as  an  alternating  motor  by  feeding  alter- 
nating current  into  the  collecting  rings  and  bringing  the 
machine  into  syncronism  by  any  convenient  means,  there 
will  evidently  be  flowing  through  the  armature  windings 
the  same  sort  of  current  that  would  be  generated  if  the 
armature  were  working  as  a  dynamo.  As  a  dynamo  this 
current  could  either  be  withdrawn  through  the  rings  as 
alternating  current  or  through  the  commutator  as  continu- 
ous current.  So  when  the  same  current  is  delivered  to  the 


170    POWER   DISTRIBUTION    FOR   ELECTRIC   RAILROADS. 

machine  from  an  external  source  it  may  be  taken  off  the 
commutator  as  continuous  current  or  off  the  rings  as  alter- 
nating  current  if  continuous  current  be  supplied  from  the 
line.  The  commutator  neither  knows  nor  cares  whether 
the  current  that  comes  to  its  leads  is  generated  in  the  arm- 
ature or  poured  into  it  from  a  distant  source.  A  small 
part  of  the  energy  supplied  is  expended  in  keeping  up  the 


FIG.  89. 

rotation  of  the  machine  as  a  motor,  the  rest  is  delivered  to 
the  line  as  available  current. 

This  device  furnishes  a  very  beautiful  and  efficient 
method  for  the  conversion  of  alternating  current.  It  is 
most  available  for  practical  purposes  in  its  polyphase  form, 
since  although  it  works  admirably  with  single-phase  cur- 
rent it  cannot  start  as  a  motor,  nor  is  it  able  to  give  quite 
so  good  an  output.  For  polyphase  work  the  armature 
winding  is  tapped  not  as  in  Fig.  72  at  two  points,  but  at 
three  or  more,  so  spaced  as  to  divide  the  windings  in  such 
wise  that  if  the  armature  were  worked  as  a  dynamo  it 
would  deliver  polyphase  currents. 

Fig.  90  shows  the  connections  of  a  two  pole  ring  winding 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS.          1 71 

tapped  for  three-phase  currents  or  for  working  as"  a  three- 
phase  rotary  converter.  Here  leads  are  simply  taken  off  from 
three  points  on  the  winding  1 20  degs.  apart  and  carried  to 
the  three  collecting  rings.  In  this  case  the  machine  will  come 
up  to  speed  as  a  three-phase  motor  when  the  field  is  broken 
and  current  thrown  on  the  rings.  Many  rotary  converters, 
however,  require  a  very  large  starting  current  and  in  start- 
ing greatly  reduce  the  voltage  of  the  circuit,  so  that  induc- 
tion motors  are  sometimes  employed  to  bring  them  to  syn- 
chronous speed,  or  where  several  rotaries  are  used,  the 
machines  are  generally  started  from  the  continuous  current 
side.  When  at  speed  the  field  circuit,  which  is  connected 
like  that  of  an  ordinary  shunt  dynamo,  is  made,  the  armature 
falls  into  synchronism  with  the 
generator  and  continuous  current 
may  be  drawn  from  the  commuta- 
tor. For  two  phase  currents  the 
leads  are  taken  off  in  a  precisely 
similar  way,  but  from  four  points 
90  degs.  apart  on  the  winding. 

There  are  still  other  and  more  complicated  connections 
used  for  multipolar  machines  and  for  various  practical  reas- 
ons, but  they  all  embody  the  same  general  principles. 

As  a  matter  of  fact  the  rotary  converter  has  in  efficiency 
or  output  an  advantage  over  the  same  structure  used  as  a 
dynamo  since,  as  inspection  of  the  winding  will  show,  the 
average  loss  in  the  armature  is  lessened,  because  the  current 
does  not  at  all  times  have  to  traverse  the  full  extent  of 
the  winding  between  ring  and  ring. 

An  excellent  example  of  modern  practice  in  the  rotary 
converter  line  is  the  Westinghouse  two  phase  machine 
shown  in  Fig.  9 1 ,  designed  especially  for  railway  substa- 
tion working.  As  a  generator  it  can  deliver  either  two 
phase  or  continuous  currents  or  both,  or  when  two  phase 
current  derived  from  reducing  transformers  is  supplied 
to  the  collecting  rings,  continuous  current  at  from  500  to 
550  volts  can  be  withdrawn  from  the  commutator.  The 
striking  similarity  between  this  and  an  ordinary  railway 
generator  is  at  once  apparent,  and  in  practical  properties 


172     POWER  DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

the  two  machines  are  almost  identical.  In  fact  the  earli- 
est rotary  converters  were  made  by  adding  rings  to  stand- 
ard generators,  but  of  late  some  modifications  have  been 
found  useful.  The  three  phase  rotary  converter  has 
already  been  shown  in  connection  with  the  Lowell  plant. 
All  rotary  converters  require  alternating  current  of 
less  voltage  than  the  continuous  current  derived  from  it. 


«5r,  flY  JOURNAL 


FIG.   91. 

The  exact  voltage  varies  with  the  number  of  phases  used 
and  with  the  field  excitation  of  the  converter.  In  the  two 
and  three  phase  machines  ordinarily  used  the  alternating 
voltage  ranges  from  300  to  375  for  a  continuous  voltage  of 
500  to  550. 

The  efficiency  of  conversion  by  this  means  is  very 
high,  at  least  as  great  as  would  be  obtained  from  standard 
railway  dynamos  of  similar  size  and  speed,  and  the  con- 
verters as  a  rule  work  admirably.  If  the  voltage  per  com- 
mutator segment  is  kept  within  conservative  limits  and  the 
armature  inductance  is  moderate,  converters  give  no  trouble 


TRANSMISSION  OF  POWKR  FOR  SUBSTATIONS.       173 

from  sparking  and  require  very  little  attention.  They  are 
usually  for  rather  low  frequency,  twenty-five  to  thirty-five 
cycles  per  second,  owing  to  the  fact  that  a  higher  frequency 
necessitates  a  rather  complicated  commutator  in  order  to 
keep  the  volts  per  bar  sufficiently  low,  and  this  condition 
makes  the  design  of  the  armature  somewhat  embarrassing, 
especially  in  very  large  low  speed  machines. 

As  in  the  case  of  synchronous  alternating  motors,  the 
strength  of  the  field  in  a  rotary  converter  has  a  profound 
influence  on  the  voltage  of  the  alternating  line  and  can 
cause  the  current  therein  to  lag  or  lead  by  a  considerable 
amount.  The  proper  adjustment  of  the  field  strength  is  a 
very  important  matter.  It  should  be  so  arranged  as  to  keep 
the  line  current  as  nearly  in  phase  as  possible,  which  is 
probably  best  accomplished  by  using  generators  and  con- 
verters of  low  inductance  and  compounding  them. 

The  rotary  converter  is  the  best  means  at  present 
available  for  obtaining  continuous  from  alternating  cur- 
rents. Its  weak  points  are  the  close  interdependence  of 
the  alternating  and  continuous  voltages,  and  the  necessity 
of  using  quite  low  frequencies.  For  certain  cases  the  com- 
bined synchronous  motor  and  generator,  in  principle  like 
Fig.  89,  may  be  advantageous,  but  for  all  around  working, 
the  rotary  converter  is  generally  preferred. 

Power  transmission  lines  for  alternating  current  re- 
quire rather  more  care  in  computation  than  do  continuous 
current  lines,  for  one  has  to  deal  with  the  phenomena  of 
inductance  in  line  and  load,  and  the  resulting  ' '  false  cur- 
rent" which  may  compel  the  delivery  of  a  current  greater 
than  is  indicated  by  the  energy  concerned. 

In  the  general  problem  of  power  transmission  these 
considerations  are  most  troublesome,  but  when  the  princi- 
pal work  is  the  operation  of  substations  for  railway  pur- 
poses, which  is  the  case  in  hand,  it  becomes  comparatively 
simple. 

For  since  changing  the  excitation  of  a  synchronous 
alternating  motor  shifts  the  phase  of  the  line  current,  this 
excitation  can  be  adjusted  so  as  to  neutralize  the  induct- 


174  POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 


in  circuit  and  leave  the  line  current  nearly  or  quite 
in  phase  with  its  K.  M.  F. 

As  the  motor  field  is  gradually  strengthened,  the  cur- 
rent lags  less  and  less,  the  apparent  energy  comes  to  ap- 
proximate more  closely  the  real  energy,  and  the  current 
on  the  line  consequently  grows  smaller.  When  the  lag 
disappears  the  apparent  energy  (i.  e.  volts  multiplied  by 
amperes)  coincides  with  the  real  energy,  and  the  line  cur- 
rent is  a  minimum.  As  the  motor  field  is  strengthened 
still  more,  the  current  begins  to  lead  the  E.  M.  F.,  the  ap- 
parent energy  increases,  and  the  line  current  also  in- 
creases. 

It  is  desirable  to  keep  the  power  factor  of  the  circuit 
(i.  e.,  the  ratio  between  real  and  apparent  energy)  as  near 
unity  as  possible,  since  when  this  condition  is  fulfilled  the 
energy  delivered  per  ampere  of  line  current  is  a  maximum, 
and  all  the  apparatus  gives  its  best  performance.  Hence, 
the  field  of  the  motor  or  converter  should  be  kept  at  such  a 
point  that  the  line  current  for  normal  output,  as  shown  by 
the  ammeter,  shall  be  a  minimum. 

As  the  output  varies,  the  current  will  lag  or  lead 
•somewhat,  but  if  the  output  for  which  the  lag  vanishes  is 
properly  chosen,  the  power  factor  at  all  working  loads  will 
still  be  high,  say,  within  ten  per  cent  of  unity. 

The  net  result  of  the  adjustment  of  the  motor  field 
with  reference  to  the  inductance  in  circuit  is  practically  the 
maintenance  of  a  power  factor  very  near  unity  under  all 
normal  conditions,  so  that  the  circuit  behaves  almost  as  if 
it  were  carrying  continuous  current.  Kxcept  for  a  small 
allowance  for  changes  in  the  power  factor  the  line  may  be 
computed  much  like  a  continuous  current  line.  In  fact 
the  formulae  of  Chap.  I  may  be  used  unchanged  for  fig- 
uring single  phase  and  two  phase  transmission  circuits, 
assuming  that  C  in  these  formulae  equals  the  watts  deliv- 
ered divided  by  the  voltage  of  delivery,  as  with  continuous 
current. 

If,  for  example,  we  wish  to  deliver  450  k.w.  100,000 
ft.  from  our  station,  using  10,000  volts  on  the  line  with  ten 


TRANSMISSION   OF   POWER   FOR   SUBSTATIONS.          175 

per  cent  drop,  the  equivalent  current  is  fifty  amperes  and 
we  may  proceed  as  follows: 

From  formula  ( i )  Chap.  I 

i iX  so X 200,000 
c.  m.  = —    ° =  110,000. 

IOOO 

This  gives  the  size  of  wire  necessary  for  a  single  phase  cir- 
cuit.    If  the  circuit  is  two  phase,  half  of  the  energy  is  sent 
over  each  circuit,  which  must  be  then  of  55,000  c.  m.  wire. 
From  formula  (5) 

w = 33X50X40,000 = 66>000  ibs, 

IOOO 

This  amount  is  the  same  for  both  the  two  phase  and  single 
phase  circuits,  in  the  way  usually  employed  for  operating 
two  phase  circuits,  i.e.,  a  complete  and  independent  circuit 
for  each  phase.  Sometimes  the  two  phases  have  a  common 
wire  which  modifies  the  amount  of  copper  required,  but 
this  method  of  interconnection  is  seldom  used  on  a  large 
scale,  since  on  long  lines  and  at  high  voltages  it  involves 
serious  practical  difficulties. 

The  three  phase  system  requires  a  special,  though  very 
simple,  calculation  for  the  line.  As  ordinarily  installed 
the  three  phases  are  mutually  interconnected,  so  that  the 
line  consists  of  only  three  wires.  This  combination  of  cir- 
cuits so  utilizes  the  wire  that  for  a  given  amount  of  energy 
delivered  with  a  given  maximum  voltage  between  lines 
and  at  a  given  loss,  the  copper  required  is  just  seventy-five 
per  cent  of  that  necessary  for  an  equivalent  single  phase 
line. 

This  means  that  since  the  three  phase  line  consists  of 
three  equal  wires  stretching  from  station  to  station,  each  of 
these  wires  must  be  of  half  the  cross  section  needed  for  a 
single  phase  line  wire  under  similar  circumstances.  If  the 
single  phase  line  consists  of  two  wires  each  weighing  1000 
Ibs.  per  mile,  the  three  phase  line  will  consist,  for  the  same 
loss,  of  three  wires  each  weighing  500  Ibs.  per  mile. 

There  are,  of  course,  divers  ways  of  taking  ac- 
count of  this  saving  in  the  formulae,  but  the  author  has 


176     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 


found  the  following  to  be  the  most  convenient  and  direct. 
Write  in  (i)  —for 
tions,  for  L.     Then 


Write  in  (i)  —for  C,  and  D,  the  distance  between  sta 


„'» 

...  ---  _ 

K  being  as  before  the  loss  in  volts,  while  W  is  watts  de- 
livered and  V  voltage  of  delivery. 

Applying  this  formula  to  the  example  just  given  we 
have 

ft  m.  =  "X  50  X  100,000  = 

1000 

This  is  the  area  of  each  of  the  three  wires.  Similarly  for 
the  total  weight  we  may  modify  (5)  and  multiply  by  3,  giv- 
ing for  a  close  approximation  the  exceedingly  simple  form 

100 


Applying  this  to  the  case  in  hand  we  have 

w  =  100X50X10,000  =       lb 

1000 

A  very  simple  formula  for  approximate  cost  is 


B 

wherein  P  is  the  total  cost  in  dollars  and  p  the  current 
price  of  bare  copper  in  cents  per  pound. 

These  formulae  for  alternating  transmission  -circuits 
enable  the  economics  of  the  matter  to  be  investigated  very 
rapidly.  In  the  final  design  of  the  line  it  will  usually  be 
found,  as  in  the  case  given,  that  the  size  of  wire  will  fall  be- 
tween two  standard  sizes.  In  this  case,  as  a  rule,  select  the 
nearest  size  and  figure  out  the  final  amount  of  copper  from 
the  actual  weight  of  this  wire. 

If  the  excitation  of  the  motor  or  rotary  converter 
fields  is  properly  adjusted  no  account  need  be  taken  of  in 


TRANSMISSION   OF   POWER    FOR   SUBSTATIONS.       177 

ductive  drop,  since  the  widest  departure  of  the  power 
factor  from  unity  will  not  in  any  practical  case  be  great 
enough  to  disturb  the  working  voltage  seriously. 

The  only  time  at  which  inductance  is  much  in  evi- 
dence is  during  the  periods  of  starting  the  motors  or  ro- 
tary converters.  For  the  best  results  the  generators  should 
have  good  inherent  regulation  so  that  lagging  current  will 
not  reduce  the  voltage  seriously  and  it  is  well  to  raise  the 
initial  voltage  a  little  at  the  time  of  starting.  Rotary 
converters  when  thrown  into  action  may  assume  either 
polarity,  but  a  few  tentative  touches  of  the  switch  with 
small  current  will  secure  an  K.  M.  F.  in  the  right  direc- 
tion or  better,  one  may  start  them  from  direct  current. 

Both,  polyphase  generators  and  rotary  converters  oper- 
ate well  in  parallel,  behaving,  in  fact,  much  like  continu- 
ous current  generators,  when  they  are  once  in  adjustment. 
The  process  of  throwing  alternators  in  parallel  is  very 
simple  if  one  remembers  that  the  currents  must  be  in 
phase  as  well  as  of  the  same  voltage  at  the  moment  of  con- 
nection. The  former  condition  is  determined  by  phase 
lamps,  the  latter  by  the  voltmeters. 

For  general  transmission  for  railway  work  the  voltage 
should  generally  be  from  5000  to  10,000,  more  often  the 
latter.  In  favorable  climates  even  higher  pressures  may 
be  safely  employed.  The  best  field  for  such  power  trans- 
mission is  in  cases  of  distribution  over  distances  of  fifteen 
miles  and  upwards  under  circumstances  in  which  a  specially 
favorable  spot  can  be  selected  for  the  main  generating 
station. 

When  alternating  motors  can  be  conveniently  em- 
ployed on  the  cars,  transmission  from  a  central  station  at 
high  voltage  may  become  the  rule  instead  of  the  exception, 
for  with  power  delivered  to  the  working  conductors  from 
static  transformers  requiring  no  attention  there  will  be  less 
excuse  for  long  and  heavy  feeders.  In  the  next  chapter 
we  will  consider  the  application  of  alternating  motors  to 
service  on  cars  and  the  relation  of  this  practice  to  the 
development  of  long  distance  electric  lines. 


CHAPTER  VII. 

ALTERNATING   MOTORS   FOR   RAILWAY  WORK. 

Avast  amount  of  money,  time,  and  ingenuity,  has  been 
spent  in  attempts  to  develop  motors  for  alternating  current 
good  enough  to  replace  continuous  current  motors  in  all 
their  varied  uses.  These  attempts  have  led  to  many  fail- 
ures, but  through  them  all  we  have  come  at  the  present 
time  to  a  very  gratifying  measure  of  success.  But  rail- 
way service  is  on  the  whole  the  severest  work  to  which 
any  motor  can  be  put,  for  it  involves  severe  strains  in 
starting,  heavy  loads  on  grades,  constant  and  severe  shocks 
and  jarring,  and  exposure,  usually,  to  dust  and  moisture. 
Beyond  this  a  railway  motor  must  be  easily  reversible,  and 
must  be  able  to  work  week  in  and  week  out  without  close 
attention  or  frequent  overhauling. 

Until  very  recently  these  difficulties  have  deterred 
engineers  from  any  serious  attempts  to  put  into  use  alter- 
nating motors,  but  the  development  of  electric  railway  sys- 
tems into  conditions  that  demand  the  methods  and  appar- 
atus of  long  distance  power  transmission  has  forced  the 
alternating  motor  into  consideration.  We  have  just  seen 
the  nature  of  substation  distribution  for  continuous  current 
railway  motors,  and  to  tell  the  truth  it  leaves  much  to  be 
desired.  The  losses  of  energy  incurred  in  passing  from  alter- 
nating to  continuous  current  are  at  best  rather  serious,  the 
apparatus  for  the  purpose  is  a  very  considerable  item  of 
expense  and,  what  is  worse,  a  substation  with  rotary  con- 
verters requires  constant  attention,  so  that  the  cost  of  at- 
tendance, to  say  nothing  of  repairs  and  depreciation  on  sub- 
station equipment,  makes  transmitted  power  so  expensive 
as  to  bar  it  from  the  general  use  which  it  finds  when  not 
necessarily  distributed  in  the  form  of  continuous  current. 


ALTERNATING  MOTORS  FOR  RAILWAY  WORK.       179 

Power  transmission  to  rotary  converter  stations  is  there- 
fore under  existing  conditions  of  limited  applicability,  for 
purely  financial  reasons. 

With  an  available  alternating  motor  for  use  on  the 
cars  the  matter  puts  on  a  very  different  aspect.  Reducing 
transformers  would  be  placed  at  suitable  intervals  along 
the  line,  supplied  with  energy  from  high  tension  feeders 
and  feeding  the  working  conductors  directly  from  their  sec- 
ondaries. The  rotary  converters  or  equivalent  machines, 
with  the  accompanying  apparatus,  the  substation  itself  and 
all  the  attendance  would  be  dispensed  with.  In  addition, 
the  energy  lost  in  conversion  to  continuous  current — from 
ten  to  twenty  per  cent  of  the  whole — would  be  saved.  As- 
suming one  hundred  kilowatts  average  output  in  the  sub- 
station, working  twenty  hours  per  day,  the  actual  saving 
would  amount  to  not  less  than  half  a  cent  per  kilowatt 
hour,  $36.50  per  kilowatt  per  year.  The  abolition  of  this 
charge  for  the  conversion  of  energy  to  continuous  current 
would  make  power  distribution  from  a  central  station  pay 
in  a  large  number  of  cases  where  boosters  or  separate 
generating  stations  are  now  the  most  economical  methods 
available. 

Furthermore  it  would  make  it  possible  to  employ  water 
power  far  more  freely  than  is  at  present  worth  the  while, 
and  would  give  a  particular  impetus  to  long  interurban 
and  cross  country  lines  now  hampered  by  the  heavy  cost  of 
transmitting  the  necessary  power. 

Admirable  as  is  this  outlook  we  must  not  for  a  moment 
lose  sight  of  the  fact  that  before  entering  this  promised 
land  we  must  have  an  alternating  motor  substantially  as 
efficient  and  durable  as  the  present  standard  railway 
motors. 

It  is  not,  however,  necessary  that  there  should  be  any 
striking  similarity  in  appearance  or  in  methods  of  opera- 
tion between  the  two  types  of  motor,  or  even  that  the  al- 
ternating motor  should  be  suited  to  all  conditions  under 
which  continuous  current  motors  are  now  worked.  Alter- 
nating and  continuous  currents  have  found  for  themselves 


180     POWER   DISTRIBUTION    FOR   ELECTRIC   RAILROADS. 

distinct  fields  of  usefulness  in  electric  lighting — why  not 
also  in  electric  railroading  ? 

Out  of  the  motley  throng  of  alternating  motors  four 
types  are  fairly  possible  for  application  to  railway  practice. 
Each  is  characterized  by  a  combination  of  good  and  bad 
qualities  somewhat  difficult  to  evaluate  in  the  present 
state  of  our  knowledge  of  alternating  railway  work.  We 
may  tabulate  the  types  in  question  as  follows: 

I.  Synchronous  motors  started  by  commutation. 
II.  Synchronous  motors  started  as  induction  motors. 

III.  Asynchronous  polyphase  motors. 

IV,  Asynchronous  monophase  motors. 

The  first  two  classes  have  exceedingly  valuable  properties 
for  certain  purposes,  but  are  not  suited  for  railway  work 
requiring  very  frequent  stopping  and  starting  or  constant 
variation  of  speed. 

The  third  class  can  meet  all  requirements  as  to  starting 
torque  and  speed  variation,  and  can  be  made  substantially 
as  efficient  and  durable  as  continuous  current  motors,  but 
requires  a  somewhat  troublesome  system  of  working  con- 
ductors. 

The  fourth  class  starts  moderately  well,  is  somewhat 
weak  at  present  in  the  matter  of  speed  variation,  but  can 
be  operated  on  existing  systems  of  working  conductors. 

I.  It  is  a  well  known  fact  that  a  series  wound  motor 
with  fields  laminated  to  check  eddy  currents  will  start  and 
run  fairly  well  on  an  alternating  circuit,  particularly  if  the 
frequency  is  low.  The  late  Mr.  Kickemeyer  produced  a 
motor  of  this  class  which  gave  admirable  starting  torque 
and  ran  with  a  good  degree  of  efficiency.  The  practical 
difficulty  that  has  hindered  the  commercial  development  of 
such  motors  is  rather  severe  sparking,  which  seems  to  be 
irremediable  and  if  long  continued  does  serious  damage  to 
the  commutator. 

If,  however,  the  sparking  only  occurs  during  the  pro- 
cess of  starting  it  is  not  a  difficult  matter  to  avert  injury  to 
the  commutator,  so  that  if  such  a  motor  can  be  worked 
normally  as  a  synchronous  alternating  machine,  and  as  a 


OF    TVIK 

UNIVERSITY 


ALTERNATING   MOTORS    FOR   RAILWAY   WORK.          l8l 

series  commutating  motor  only  at  starting,  it  become  cap- 
able of  doing  excellent  work. 

There  are  divers  other  means  of  starting  an  alternat- 
ing motor  by  means  of.  a  commutator.  A  commutated 
field  in  shunt  to  the  armature  can  be  made  to  give  a  power 
of  starting  sufficient  to  bring  an  unloaded  motor  up  to  syn- 
chronous speed,  and  in  fact,  an  ordinary  compound  wound 
alternator  can  be  made  self  starting  by  means  of  its  com- 
pounding commutator.  These  devices  do  not  permit  of 
starting  under  anything  much  exceeding  friction  load  and, 
hence,  are  inferior  for  severe  work  to  the  series  starting 
device  just  mentioned  and  various  modifications  of  the 
same  idea. 

II.  Synchronous  motors  of  the  polyphase  type  are 
capable  of  starting  fairly  well  as  induction  motors,  the  field 
poles  serving  as  armature.  When  the  starting  torque  is 
obtained  merely  from  eddy  currents  in  the  pole  pieces,  as 
in  most  synchronous  motors  and  rotary  converters,  the 
torque  is  weak  and  the  starting  current  abnormally  large. 
To  secure  a  quarter  of  the  full  load  running  torque,  fully 
twice  the  full  load  current  would  be  ordinarily  required, 
or  proportionally  less  if  the  motor  is  starting  under  merely 
friction  load. 

It  is  quite  possible,  however,  to  construct  a  specialized 
field  with  inductive  windings  in  the  pole  faces,  so  that  the 
the  motor  will  give  its  full  normal  torque  at  starting  on  a 
current  not  greatly  in  excess  of  its  full  load  current,  and 
will  be  capable  of  shifting  over  to  synchronous  run- 
ning when  up  to  speed. 

In  a  similar  way  a  monophase  motor  could  be  arranged 
to  be  self  starting  as  an  induction  motor  and  then  trans- 
formed to  the  synchronous  type. 

For  starting  under  load  these  forms  are  probably  in- 
ferior to  those  starting  as  series  motors  by  commutation, 
out  they  are  simpler  and  sufficient  for  starting  unloaded. 

To  ordinary  street  railway  service  with  constant  stop- 
ping and  starting  under  all  sorts  of  unfavorable  conditions, 
these  essentially  synchronous  motors  are  inapplicable, 


1 82     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

since  they  do  not  start  well  enough  and  are  incapable  of 
speed  variation  when  running  in  synchronism.  Neverthe- 
less, they  are  not  to  be  despised  for  certain  classes  of  rail- 
way work  to  which  we  must  look  forward. 

For  long  lines  with  stops  only  at  stated  stations  such 
motors  can  even  now  be  made  available.  If  starting  by 
clutch  be  considered  inadvisable  there  is  now  no  serious 
difficulty  in  the  way  of  a  commutating  start  quite  good 
enough  to  bring  a  train  up  to  speed.  Once  in  synchronism 
the  motors  would  drive  steadily  ahead  up  grade  and  down 
at  a  uniform  speed  until  the  next  station  was  reached. 
The  longer  the  line  and  the  fewer  the  stops  the  better 
would  be  the  operation  of  the  system. 

The  great  advantage  in  synchronous  motors  for  such 
work  lies  in  their  freedom  from  lagging  current,  and 
their  insensitiveness  to  changes  of  voltage.  A  power  factor 
approaching  unity  such  as  can  readily  be  obtained  from 
large  synchronous  motors  reduces  the  difficulties  of  trans- 
mission very  materially,  and  particularly  it  diminishes  the 
necessary  capacity  in  the  generating  station  and  in  the 
line. 

In  general  transmission  plants  for  a  mixed  load  of 
lights,  synchronous  and  induction  motors,  the  power 
factor  can  be  kept  fairly  high,  with  careful  operation  prob- 
ably up  to  .85  or  .90.  This  power  factor  means  that  for 
operation  at  a  given  voltage  ten  to  fifteen  per  cent 
more  current  must  be  generated  and  transmitted  than  cor- 
responds to  the  energy  delivered.  In  addition  a  similar 
amount  of  reserve  voltage  must  be  available  to  compensate 
for  the  inductive  drop  in  the  line  and  the  reaction  of  the 
lagging  current  in  the  generators. 

The  total  net  effect  then,  of  even  this  power  factor  is 
to  call  for  not  less  than  twenty-five  per  cent  extra  capacity 
in  the  generating  plant.  Were  it  not  for  the  fact  that 
polyphase  generators  have  a  high  output  compared  with 
continuous  current  generators,  even  this  increase  would 
be  serious — as  it  is  it  is  annoying.  In  plants  operating 
induction  motors  only,  the  increased  capacity  necessary  by 
reason  of  lagging  current  may  be  very  much  more  serious, 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK.          183 

and  makes  the  synchronous  motor  a  thing  not  lightly  to 
be  put  aside  as  impracticable. 

III.  Although  the  asynchronous  polyphase  motor  is 
now  not  unfamiliar  and  its  theory  is  fairly  well  known  to 
most  engineers,  its  practical  characteristics  are  not  widely 
understood. 

We  may  best  regard  it  as  an  alternating  motor  in 
which  the  current  is  led  into  the  armature  by  induction  as 


FIG.  93. 

in  an  ordinary  transformer  instead  of  by  brush  contacts. 
Its  field  and  armature  windings  are  so  organized  that  the 
currents  in  them  bear  to  each  other  the  relation  necessary 
to  secure  effective  torque,  as  in  any  other  motor.  Whether 
the  windings  which  deliver  current  to  the  armature  are  used 
alternately  for  this  purpose  and  for  establishing  a  field 
with  which  the  induced  current  can  react,  or  whether  in- 
ducing and  field  windings  are  specialized;  whether  the 
structure  is  so  disposed  that  there  is  a  true  resultant  rotary 
magnetization  or  whether  there  exists  a  rotary  pole  only  in 
the  sense  in  which  the  poles  rotate  in  a  continuous  current 


184   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

armature — all  these  are  questions  which  have  but  a  trivial 
bearing  on  the  actual  properties  of  the  machines.  As  a 
matter  of  fact  induction  motors  are  much  closer  in  prin- 
ciples and  properties  to  continuous  current  motors  than  is 
generally  supposed.  Like  shunt  motors  they  tend  to  run 
at  a  constant  speed  and  when  the  load  changes  they  speed  up 
or  slow  down  just  enough  to  permit  enough  armature  cur- 
rent to  flow  to  adjust  the  motor  to  the  new  conditions  of 
load.  Like  shunt  motors  too,  they  require  at  starting  a  re- 
sistance in  the  armature  circuit  to  keep  the  starting  cur- 
rent within  bounds. 

Their  general  properties  are  very  little  influenced  by 
the  number  of  phases  for  which  they  are  wound.  There 
is  supposed  to  be  a  slight  increase  of  output  with  increase 
in  the  number  of  phases,  but  as  in  the  case  of  multipolar 
continuous  current  machines  the  increased  output  is  more 
a  matter  of  finesse  in  design  than  it  is  dependent  on  any 
theoretical  considerations. 

At  the  present  time  all  polyphase  induction  motors  are 
strikingly  alike  in  structural  features.  With  very  few  ex- 
ceptions they  consist  of  two  concentric  annular  masses  of 
laminated  iron,  of  which  the  inner  one  is  supported  on  the 
shaft  and  is  free  to  rotate,  while  the  outer  one  is  carried  by 
the  frame  of  the  machine.  The  outer  face  of  the  inner 
ring  and  the  inner  face  of  the  outer  ring  are  provided  with 
slots  or  holes  to  receive  the  windings.  Fig.  93  shows  the 
character  and  relation  of  these  rings.  The  slots  or  holes 
are  various  in  number  and  shape,  but  those  in  the  two 
members  are  different  in  number  to  keep  the  magnetic  re- 
lations constant  irrespective  of  the  position  of  the  rotating 
member.  The  teeth  are  very  seldom  developed  into  any- 
thing approaching  projecting  pole  pieces,  unless  in  small 
motors,  as  it  is  desirable  to  distribute  the  windings  as  uni- 
formly as  possible.  In  American  motors,  the  slots  are  usu- 
ally open,  in  Kuropean  types  the}7  are  frequently  closed  as 
shown. 

Both  rings  are  supported  in  a  suitable  frame.  In  one 
set  of  slots  is  wound  the  primary  inducing  winding,  in  the 
other  the  secondary  or  induced  current  winding.  Some- 


ALTERNATING  MOTORS  FOR  RAILWAY  WORK. 


1 85 


times  one  winding  rotates,  sometimes  the  other.  Conven- 
tionally we  call  the  primary  member  the  field  and  the  sec- 
ondary member  the  armature. 

Fig.  94  shows  a  fifty  horse  power,  two  phase  induction 
motor  of  a  recent  design  and  gives  an  admirable  idea  of  the 
way  in  which  such  a  machine  is  constructed.  In  this  case 
the  field  revolves,  while  the  armature  is  stationary.  The 
working  current  is  led  into  the  field  through  the  three  col- 
lecting rings  just  outside  the  bearing,  the  two  phases  being 
given  a  lead  in  common  at  the  motor.  This  revolving  field 


FIG.  94 


construction  has  several  well  marked  advantages.  The 
primary  element  in  which  the  heaviest  hysteretic  loss  occurs 
is  reduced  to  the  smallest  practicable  dimensions.  The 
secondary  being  stationary  can  have  resistance  put  in  series 
with  it  through  ordinary  binding  posts,  sometimes  a  great 
convenience,  and  since  the  secondary  winding  is,  as  shown, 
very  simple,  the  armature  can  be  split  like  the  field  of  a 
dynamo  and  the  upper  half  lifted  off  to  permit  inspection 
or  removal  of  the  revolving  field.  As  the  clearance  in  iu- 


)86   POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

duction  motors  is  usually  very  small,  }$  in.  or  less,  such  an 
arrangement  is  very  convenient. 

Fig.  95  shows  a  fine  three  phase  motor  of  125  h.  p.,  in 
which  the  armature  revolves  while  the  field  is  stationary. 
The  main  leads  are  taken  to  the  connection  board  on  the 
top  of  the  motor,  and  there  are  no  moving  contacts  what- 
ever. The  resistance  used  in  starting  the  motor  is  stowed 
inside  the  armature  ring  and  its  terminals  brought  out  to 
three  contacts  secured  to  the  armature  spider.  When  the 


FIG.  95. 

motor  is  up  to  speed  these  are  short  circuited  by  a  solid 
ring  slipped  a  couple  of  inches  along  the  shaft  by  the  small 
handle  shown  alongside  the  bearing.  Sometimes  this  re- 
sistance is  in  two  or  more  sections,  successively  short  cir- 
cuited by  a  similar  motion  of  the  ring.  This  arrange- 
ment does  away  once  for  all  with  all  moving  contacts.  The 
field,  being  stationary,  can  be  safely  wound  for  higher 
voltages  than  if  it  were  rotating  and  suffers  less  mechani- 


ALTERNATING  MOTORS  FOR  RAILWAY  WORK.       187 

cal  strain  at  all  voltages.  The  machine  thus  requires  very 
little  attention,  and  besides  is  quite  free  from  all  danger  of 
sparking,  sometimes  a  very  undesirable  possibility. 

Both  the  constructions  shown  have  merits  for  special 
purposes.  The  revolving  armature  arrangement  gives  a 
simpler  and  safer  machine  for  most  ordinary  purposes,  and 
especially  for  high  voltage  work  without  transformers. 
The  revolving  field  is  the  better  for  very  large  motors  and 
for  all  work  requiring  considerable  and  variable  resistance 
in  the  armature  circuit.  It  is  therefore,  particularly  well 
adapted  for  railway  work  at  varying  speed,  hoisting  and 
similar  severe  service.  In  general  properties,  efficiency, 
power  factor,  regulation  and  so  forth  the  two  construc- 
tions are  indistinguishable. 

For  effectively  meeting  the  demands  of  railway  service 
a  motor  must  be  simple,  durable  and  easy  to  inspect  and 
repair;  it  must  also  be  capable  of  regulation  in  speed  with- 
in rather  wide  limits,  must  have  great  initial  torque,  and 
must  have  a  good  efficiency.  The  first  three  mechanical 
qualifications  the  induction  motor  is  amply  able  to  meet. 

The  simplicity  of  the  structure  has  already  been  set 
forth.  The  nature  of  the  field  winding  is  well  shown  in  Fig. 
96,  the  field  of  a  slow  speed,  two  phase  motor  of  one  hundred 
horse  power  output,  and  the  winding  is  for  2000  volts.  In 
ordinary  American  practice  the  field  coils  are  in  open  slots 
so  that  they  can  be  the  more  readily  repaired  or  replaced. 
The  armature  winding  is  usually  of  massive  bars  with 
heavy  end  connections  and  is  well  exhibited  in  Fig.  94. 
The  matter  of  durability  is  best  settled  by  experience. 
During  the  past  seven  years  there  have  been  put  in  opera- 
tion in  this  country  polyphase  induction  motors  aggregat- 
ing more  than  5o,oooh.  p.  in  output;  and  from  the  author's 
own  personal  knowledge  it  may  be  said  that  the  repairs 
upon  these  have  been  almost  negligible,  far  smaller  than 
in  any  other  class  of  moving  electrical  machinery.  This 
is  a  strong  statement,  but  it  is  fully  borne  out  by  the 
facts. 

Speed  regulation  in  polyphase  induction  motors  is  ef- 
fected by  means  not  unlike  those  used  for  continuous  cur- 


1 88     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

rent  motors.  A  common  shunt  motor  may  have  its  speed 
varied  in  two  very  simple  ways.  First,  the  field  strength 
may  be  changed;  second,  the  armature  current  may  be  cut 
down  by  a  rheostat.  A  series  wound  motor  may  be  simi- 
larly governed  by  changing  the  field  strength  or  changing 
the  voltage. 


FIG.  96. 

In  an  induction  motor  the  same  devices  are  used  in  a 
somewhat  different  way.  Weakening  the  field  of  such  a 
motor  by  reducing  the  voltage  of  supply  causes  the  arma- 
ture to  run  slower,  but  since  the  armature  current  is  sup- 
plied by  the  field  as  a  transformer  the  armature  is  also 
greatly  weakened  and,  hence,  the  torque  falls  off  very  rap- 
idly as  the  voltage  is  lowered.  Modifying  the  armature 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK.          189 


strength  by  a  rheostat  in  circuit,  however,  cuts  down  the 
speed  until  the  added  transformer  effect  of  the  field  sup- 
plies current  enough  to  handle  the  load  at  the  new  rate  of 
speed.  By  varying  the  resistance  in  the  armature  circuit 
the  speed  can  be  varied  to  any  desired  extent,  the  torque 
remaining  constant  throughout.  Fig.  97  shows  the  speed 


10  100- 


I 

0  680- 


4+7-O— Q 


2SO--S 


13         14 


456  7          8          9         1O        11 

Speed  in  100  r-p.m. 
FIG.  97. 

variation  characteristics  of  a  fifteen  horse  power  induction 
motor  with  a  rheostat  in  the  armature  circuit.  Starting  at 
full  output  and  speed,  the  speed  was  gradually  lowered 
from  i4oor.  p.  m.  to  150  r.  p.  m.  The  torque  remained 
uniform,  so  that  the  output  was  almost  exactly  proportion- 
ate to  the  speed.  The  relation  between  them  is  shown  in 
curve  A.  The  input  meanwhile  remained  nearly  con- 
stant. B  gives  the  variation  of  the  power  factor  and  C 
shows  the  slight  and  gradual  diminution  of  the  input. 

Altogether  this  motor  behaved  almost  exactly  like  an 
ordinary  railway  motor  with  rheostatic  control,  regulating 
quite  as  well  and  with  closely  similar  inefficiency. 


1 90    POWER   DISTRIBUTION    FOR   ELECTRIC   RAILROADS. 


At  full  load  this  motor  had  about  the  efficiency  of  a 
fifteen  horse  power  motor  of  the  ordinary  kind,  but  sub- 
stantially all  the  reduction  in  output  by  lowering  the 
speed  represented  loss  of  efficiency  as  is  the  case  with  a 
series  wound,  continuous  current  railway  motor  with  rheo- 
static  control.  The  power  factor  in  this  case  was  notably 
high  at  all  speeds,  high  enough  to  cut  very  little  figure  in 
the  operation  of  the  system. 

A  car  equipped  with  motors  like  the  one  under  con- 
sideration would  handle  very  easily  as  regards  speed  varia- 


240 

220 

§200 

3 
fiiso 


20 


40        60 


80        100       120       140 
Pounds  1  Foot  Radius 


160 


180       200      220 
Street  Ry.Jourual 


FIG.  98. 


tion  and  would  give  quite  as  good  efficiency  as  hundreds 
of  cars  now  in  operation.  For  interurban  and  similar  work 
in  which  running  at  reduced  speed  is  the  exception,  the 
efficiency  would  be  all  that  can  reasonably  be  desired. 

As  regards  starting  torque,  which  for  railway  motors 
is  a  consideration  of  prime  importance,  the  modern  two  or 
three  phase  motor  leaves  little  to  be  desired.  Not  only 
will  it  start  with  very  great  torque,  but  it  will  give  this 
torque  with  relatively  less  current  than  will  a  series  con- 
tinuous current  motor.  That  such  must  be  the  case  is 
obvious  from  the  fact  that  while  the  fields  of  an  ordinary 


/*  I/TERN  ATING   MOTORS   FOR   RAILWAY  WORK.          IQI 

railway  motor  are  nearly  saturated  at  all  working  loads, 
the  fields  of  an  induction  motor  are  normally  worked  at 
low  saturation  to  avoid  hysteretic  loss,  so  that  since  the 
torque  of  a  motor  is  proportional  to  the  product  of  arma- 
ture current  and  field  strength,  doubling  the  input  in  an 
induction  motor  nearly  quadruples  the  torque.  This  is 
well  shown  in  Fig.  98,  which  gives  the  relation  between 
current  and  starting  torque  in  the  motor  referred  to  in 
Fig.  97.  The  maximum  torque  was  obtained  with  a  very 
small  resistance  in  the  armature  circuit,  which  resistance 
was  gradually  raised  to  obtain  the  other  points  in  the 
curve.  The  torque  was  truly  static  and  the  power  factor 
of  the  machine  under  this  condition  was  lower  than  when 
running  normally,  as  shown  by  the  larger  current  than  in 
Fig.  97. 

The  maximum  starting  torque,  more  than  four  times 
the  full  load  running  torque,  was  obtained  at  normal  volt- 
age by  the  use  of  about  2  ^  times  the  normal  full  load 
current. 

Four  times  the  normal  drawbar  pull  is  enough  for 
ordinary  starting  purposes  even  in  severe  street  railway 
service,  but  even  this  can  be  still  further  increased  if  nec- 
essary, by  raising  the  voltage.  The  torque,  so  long  as  the 
field  is  unsaturated,  then  increases  nearly  in  proportion  to 
the  square  of  the  applied  voltage.  Thus,  if  the  field  coils 
of  the  motor  are  in  the  star  connection  for  normal  opera- 
tion, and  are  thrown  over  to  the  mesh  connection  as  an  ex- 
treme measure,  the  applied  K.  M.  F.  per  coil  is  increased 
in  the  ratio  of  1.73:1,  and  the  resulting  torque  is  three 
times  the  normal.  This  in  combination  with  the  changes 
of  armature  resistance  indicated  in  Fig.  98,  is  enough  to  in- 
crease the  torque  enormously  in  spite  of  increasing  satura- 
tion of  the  field.  In  fact  one  can  obtain  from  an  induction 
motor  more  starting  torque  than  is  ever  called  for  in  prac- 
tical work. 

Fig.  99  shows  the  results  obtained  in  testing  a  pair  of 
three  phase  induction  motors  specially  arranged  for  rail- 
way work.  Each  motor  was  designed  to  produce  a  normal 


192     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

drawbar  pull  of  800  Ibs. ,  equivalent  at  full  car  speed  to 
about  twenty-five  horse-power.  These  machines  were 
wound  for  no  volts  between  lines,  weighed  substantially 
the  same  as  standard  railway  motors  of  the  same  output 
and  were  coupled  up  to  a  special  controller,  designed  to 
vary  both  the  armature  resistances  and  the  field  connections. 
These  connections  were  threefold,  the  mesh  or  A  for  ex- 


treme torque,  star  or  Y  for  normal  full  speed  running,  and 
' '  concatenated ' '  for  half  speeds.  The  latter  was  a  quasi  - 
series  connection  giving  much  the  same  result  as  reducing 
the  primary  voltage,  without  calling  for  special  appliances. 
It  consisted,  practically,  of  using  the  secondary  current  of 
one  motor  as  the  primary  current  of  the  other,  and  of 
course  suffered  through  adding  the  inductances  of  the  two. 
The  A  curves  refer  to  current,  the  B  curves  to  effi- 
ciency, and  the  C  curves  to  speed  of  car.  Although  the 
concatenated  connection  was  decidedly  inferior  in  efficiency , 


ALTERNATING  MOTORS  FOR  RAILWAY  WORK.       193 

both  real  and  apparent,  to  the  others,  it  still  gave  half  speed 
very  smoothly  and  with  an  efficiency  reasonably  high. 
The  drawbar  pulls  registered  were  amply  great  for  any 
service  conditions,  and  the  net  commercial  efficiency  given, 
which  includes  all  the  gearing  losses,  compares  not  unfa- 
vorably with  ordinary  continuous  currents.  The  running 
of  the  motors  was  as  good  as  could  be  desired,  and  the 
abolition  of  the  commutator  is  a  very  material  gain,  since 
collecting  rings  give  decidedly  less  trouble.  Change  of 
armature  resistance  gave  opportunity  to  pass  smoothly 
from  one  field  connection  to  another  without  jerking  the 
car.  As  appears  from  curves  C  II  and  C  III,  apparatus  of 
this  kind  has  the  very  considerable  advantage  of  fairly 
constant  speed  over  a  wide  range  of  drawbar  pull.  Al^ 
though  polyphase  induction  motors  are  termed  asynchron 
ous  they  have  so  strong  a  tendency  to  run  near  synchronous 
speed  that  they  have  the  power  of  driving  ahead  regard- 
less of  grades  unless  grossly  overloaded. 

None  of  the  methods  of  regulation  as  yet  devised  is 
quite  the  equivalent  of  the  series  parallel  control  so  exten- 
sively used  in  continuous  current  practice,  so  far  as  effi- 
ciency is  concerned.  It  is  possible  to  get,  however,  as 
complete  control  of  the  speed  and  nearly  as  good  efficiency 
at  all  except  the  lowest  speeds.  In  the  line  of  work  for 
which  alternating  motors  are  most  needed,  i.e.,  long  inter- 
urban  and  similar  lines  the  need  of  highly  efficient  control 
at  very  low  speeds  is  not  so  great  as  in  ordinary  street 
railway  work,  since  by  far  the  largest  aggregate  output  is 
at  the  higher  speeds. 

In  spite  of  the  extent  to  which  induction  motors  have 
been  used  in  the  past  seven  years,  no  important  apparatus 
is  less  generally  understood.  Even  engineers  who  are  well 
posted  in  other  matters  are  apt  to  be  dismally  ignorant  of 
the  practical  properties  of  induction  motors.  They  have 
too  often  derived  their  scant  information  from  scholastic 
papers  on  the  subject  full  of  solemn  inanities  on  the  gen- 
eral theory  of  rotating  magnetic  poles,  fortified  by  emi- 
nently respectable  equations  which  are  valuable  only  to 
those  who  know  the  limiting  conditions. 


194   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

In  point  of  fact  the  induction  motor  is  a  most  simple 
and  reliable  machine  much  closer  in  its  properties  to  con- 
tinuous current  motors  than  is  generally  supposed. 

Its  adaptation  to  railway  work  is  beset  with  fewer 
difficulties  than  confronted  the  continuous  current  motor 
a  dozen  years  ago.  The  nature  of  those  arising  from  speed 
regulation  we  have  just  considered.  The  state  of  the  case 
is  about  as  follows  :  Wherever  rheostatic  control  of  railway 
motors  is  sufficient,  the  use  of  induction  motors  presents 
no  special  difficulty,  giving  the  same  power  of  speed  reg- 
ulation upon  the  same  terms  as  in  continuous  current 
practice.  This  clears  the  way  at  once  for  much  long  dis- 
tance and  interurban  work.  In  urban  and  suburban  work 
upon  a  large  scale  something  more  is  necessary.  Several 
methods  are  available,  as  has  already  been  indicated,  con- 
catenation and  the  passage  from  mesh  to  star  connections 
being  the  most  advantageous  yet  tried.  The  application 
of  these  methods  is  now  in  the  tentative  stage,  with  the 
chances  good  for  a  favorable  result  ^when  the  work  is 
seriously  attempted.  It  should  not  be  forgotten  that 
series-parallel  control  of  regular  railway  motors  was  tried 
and  abandoned  on  account  of  forbidding  complications 
several  years  before  it  was  taken  up  again  and  pushed 
through  to  definite  success. 

Another  interesting  suggestion  for  speed  variation  is 
varying  the  number  of  motor  poles.  As  an  induction 
motor  has  no  salient  poles  this  is  a  possible  procedure,  but 
it  does  not  promise  very  good  properties  at  the  lower  speeds 
at  ordinary  frequencies.  Varying  the  impressed  E.  M.  F. 
by  reactance  in  the  primary  circuit  suggests  itself  as  the 
simplest  method  of  control.  Practically,  however,  it  leads 
to  lower  efficiency  at  all  speeds  than  the  rheostatic  control 
and  at  low  speed  the  power  factor  is  infamously  bad.  All 
these  things  will  have  to  be  threshed  out  experimentally 
as  the  present  railway  apparatus  has  been. 

The  question  of  actual  armature  speed  deserves  con- 
sideration in  this  conection.  As  a  starting  point  it  will  be 
convenient  to  remember  that  in  ordinary  practice  one  mile 


ALTERNATING   MOTORS   FOR   RAILWAY   WORK.          195 

per  hour  means  very  nearly  ten  wheel  revolutions  per 
minute.  The  usual  gear  reductions  found  in  standard 
railway  motors  range  from  about  1:4.8  to  1:3.5.  Hence 
for  a  normal  speed  of  10  miles  per  hour,  one  may  say 
roughly  that  the  armature  speed  should  be  not  over  500 
r.  p.  m.  and  would  not  probably  be  below  400  r.  p.  m.  An 
8  pole  motor  at  30  ^  would  give  at  load  say  425  r.  p.  m. , 
hence  at  speeds  below  10  miles  per  hour  some  form  of  con- 
troller would  have  to  be  used.  This  is  somewhat  awkward 
for  urban  work,  although  it  does  not  differ  materially  from 
everyday  street  railway  practice.  It  simply  means  the 
same  sort  of  inefficiency  at  low  speeds  to  which  we  have 
long  been  accustomed.  There  is  this  difference,  however, 
that  the  polyphase  motor  could  not  at  that  frequency  run 
above  10  miles  per  hour,  which  would  be  a  bit  awkward 
in  suburban  running.  Probably  a  frequency  of  40  *> 
would  prove  a  convenient  compromise,  or  a  6  pole  motor 
at  the  lower  frequency.  The  conditions  just  mentioned 
are  compatible  with  a  thoroughly  good  motor  in  other 
respects.  The  peripheral  speed  of  the  armature  would 
probably  be  somewhat  higher  than  is  usual  in  continuous 
current  railway  motors  rising  to  2500  feet  per  minute  as 
against  2000  or  thereabouts  for  a  common  railway  motor 
under  similar  conditions.  In  fast  suburban  work  these 
speeds  might  be  doubled.  There  is  no  possible  objection 
to  such  surface  velocities  for  either  kind  of  motor. 

An  utterly  foolish  opinion  is  just  now  abroad  that 
induction  motors  demand  enormous  peripheral  speeds, 
which  is  not  at  all  the  case,  as  the  above  will  show.  When 
worked  at  60  r.  or  more  it  is  convenient  to  run  the  arma- 
tures at  a  surface  velocity  of  5000  feet  or  so,  but  at  low 
frequency  it  is  quite  unnecessary. 

For  interurban  work  one  would  probably  choose  a  4 
pole  design,  giving  say,  850  r.  p.  m.  of  the  armature  at 
30  %  with  a  full  speed  of  about  20  miles  per  hour.  The 
power  to  pass  from  8  to  4  poles  or  the  reverse  would  ob- 
viously be  very  convenient,  but  the  electric  railway  was 
an  established  success  on  a  large  scale  long  before  any 


196     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

better  means  of  regulation  than  the  rheostat  was  in  use. 
It  is  perfectly  feasible  then  to  work  three-phase  motors  in 
a  precisely  similar  way  for  interurban  or  even  urban  work, 
when  conditions  make  it  desirable. 


100 


40 


.20 


20  H.  P.  3  PHASE  MOTOR 
4  POLE,  25  ro  SPEED  715  R.  P.  M 


OH.P. 


10  20 

FIG.  100. 


30 


40 


We  have  already  discussed  the  properties  of  such 
motors  somewhat,  but  a  further  examination  of  the  attain- 
able qualities  in  a  practical  motor  for  street  railway  service 
may  be  worth  the  while.  A  good  idea  of  the  performance 
of  a  well  designed  three-phase  induction  motor  of  about 
the  vSize  and  speed  required  for  railway  work  is  given  in 
Fig.  loo. 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK. 


197 


The  curves  are  from  a  4  pole,  25  ~  machine  having  a 
normal  rating  of  20  h.  p.  and  capable  of  working  up  to 
double  that  power.  The  full  load  speed  is  715  r.  p.  m. 


100  t50  200  250  300 

POUNDS  TORQUE  AT  1  FOOT  RADIUS 


FIG.  101. 


which  corresponds  to  a  car  speed  of  about  15  miles  per 
hour.  The  current  (at  220  volts)  for  full  load  is  49.7  am- 
peres, and  for  40  h.  p.,  130  amperes,  while  the  current 
running  light  is  13.55  amperes,  the  input  in  watts  being 


198    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

960.  The  power  factor  and  commercial  efficiency  are  high 
all  along  the  line,  the  former  passing  80  per  cent  at  about 
YZ  load,  rising  to  92  at  a  little  above  full  load  and  holding 
up  to  88  even  at  double  output.  The  latter  stays  above 
80  per  cent  from  6  h.  p.  to  34  h.  p.  rising  to  86  near  full 
load.  This  motor  heated  but  little,  the  field  conductors 
rising  but  4o°C,  and  the  armature  conductors  only  22°C 
after  a  full  load  running  test  of  3  h.  30  m. 

Results  even  better  than  these  can  be  attained,  as  is 
shown  in  Fig.  101.  This  is  from  an  8  pole  60  <x>  motor  of 
50  h.  p. ,  having  a  full  load  speed  of  850  r.  p.  m.  This 
latter  motor,  however,  is  operated  with  a  very  small  arma- 
ture clearance,  while  the  former  had  a  clearance  of  about 
A-  in.  For  railway  work  a  little  greater  clearance  would 
be  desirable,  about  }i  in.  The  effect  of  this  would  be  to 
lower  the  full  load  power  factor  to  about  90  per  cent  in 
each  case,  with  no  material  change  in  the  efficiency.  The 
long  and  short  of  the  matter  is  that  by  careful  design  it  is 
perfectly  feasible  to  produce  an  induction  motor  having  an 
efficiency  as  good  as  that  of  the  usual  railway  motor,  and 
a  power  factor  good  enough  to  dispose  forever  of  the  bug- 
aboo of  "  false  current,"  as  a  practical  factor  in  the  situa- 
tion. The  motor  of  Fig.  100  fitted  for  railway  use  with 
gears  and  gear  casings  weighs  about  2000  Ibs.  at  an  outside 
estimate,  which  is  not  at  all  bad  for  a  motor  of  that  capac- 
ity. One  must  remember  that  while  some  street  car  motors 
Would  show  considerably  less  weight  per  horse  power  than 
this,  they  are,  as  a  rule  allowed  pretty  stiff  heating  at 
Iheir  rated  load,  and  as  a  class  have  been  industriously 
skinned  in  the  matter  of  weight  for  the  last  ten  years. 
Street  railway  motors,  less  gears  and  cases,  usually  run 
vVom  50  to  70  Ibs.  per  h.  p.  according  to  rating,  while 
standard  induction  motors  for  stationary  service  weigh  on 
^n  average  from  65  to  70  Ibs.  per  horse  power,  sometimes 
v*own  to  60  Ibs.  or  less. 

The  effect  of  rheostatic  speed  regulation  on  the  effi- 
^iency  of  induction  motors  is  worth  a  brief  examination. 
As  regards  power  factor,  Fig.  97  gives  the  facts  in  the 


ALTERNATING   MOTORS   FOR   RAILWAY   WORK.          199 

case,  showing  that  on  the  lower  speeds  the  power  factor  is 
quite  as  good  as  at  full  speed  and  load.  The  efficiency 
as  already  stated  falls  with  the  speed,  in  fact  almost  di- 
rectly as  the  speed.  The  motor  of  Fig.  100,  giving  a  max- 
imum efficiency  of  86  should  show  about  43  per  cent  at 
half  speed  and  22  per  cent  at  quarter  speed. 

These  facts  are  set  forth  not  for  the  purpose  of  recom- 
mending induction  motors  for  indiscriminate  use  on  elec- 
tric railways,  but  to  point  out  that  induction  motors  are 
to-day  better  developed  for  such  work  than  were  the  con- 
tinuous current  railway  motors  that  built  up  the  railway 
business  eight  or  ten  years  ago.  It  is  not  too  much  to 
say  that  at  the  present  time  it  is  practicable  to  build  poly- 
phase induction  motors  quite  good  enough  for  the  entirely 
succesful  operation  of  the  long  interurban  lines  for  which 
they  are  most  needed,  and  that  their  use  would  secure 
certain  advantages  not  otherwise  to  be  obtained,  in  the 
economical  distribution  of  power. 

The  weak  points  of  polyphase  induction  motors  for 
railway  work  are  as  follows: 

I.  Necessity  for  at  least  two  trolley  wires. 

II.  Lagging  current. 

Inasmuch  as  all  true  polyphase  systems  require  at  least  three 
working  conductors,  the  best  that  can  be  done  in  supplying 
polyphase  current  is  to  utilize  the  rails  for  one  conductor 
and  provide  separate  trolley  wires  for  the  other  two.  In 
rare  instances  it  might  be  possible  to  use  a  third  rail  and  a 
single  trolley  wire  or  even  to  utilize  the  two  track  rails  as 
separate  conductors,  but  such  cases  are  likely  always  to  be 
exceptional.  In  conduit  work,  of  course,  two  working 
conductors  are  available  without  much  difficulty,  but  for 
general  purposes  the  burden  of  two  trolleys  is  difficult  to 
avoid. 

Most  street  railway  men  strongly  dislike  the  dou- 
ble trolley  in  any  form,  and  beyond  question  it  compli- 
cates the  overhead  work,  where  crossings  and  turnouts 
are  frequent,  in  the  most  frightful  manner.  Nevertheless 
even  for  city  work  it  can  be  made  steadily  operative,. 


200     POWER    DISTRIBUTION    FOR   ELECTRIC    RAILROADS. 

as  the  experience  of  some  years  in  Cincinnati  has  shown. 
The  principal  advantages  of  the  continuous  current,  double 
trolley  system  which  are  its  only  excuse  for  existence, viz., 
the  independence  of  track  condition  as  regards  motive 
power,  lessened  interference  with  other  circuits,  and  ab- 
sence of  electrolysis,  do  not  apply  with  the  same  force  to 
a  double  trolley  polyphase  system.  One  branch  of  the 
circuit  is  still  grounded  and  bad  track  contact  is  bound  to 
be  felt  in  the  operation  of  the  motors  under  some  con- 
ditions. In.  short  the  double  trolley  for  polyphase  work  is  a 
disagreeable  necessity  and  nothing  better. 

Again,  however,  comes  to  the  rescue  the  fortunate 
circumstance  that  in  much  of  the  long  distance  work  for 
which  alternating  motors  are  desirable  a  double  'trolley  wire 
is  less  objectionable  than  elsewhere. 

The  matter  of  lagging  current  is  more  serious.  Were 
all  induction  motors  possessed  of  as  good  power  factors  as 
the  one  shown  in  Fig.  97  there  would  be  no  trouble,  for  the 
lagging  current  is  too  small  to  influence  much  either  the 
capacity  of  the  plant  or  its  regulation.  But  armature 
clearance  is  a  potent  factor  in  varying  the  power  factor,  and 
the  motor  in  question  being  intended  for  hoisting  had  a 
clearance  but  little  over  ^  in.  This  is  too  small  for  the 
rough  and  tumble  work  of  electric  railroading,  and  with 
double  this  clearance,  as  in  case  of  the  motors  of  Fig.  99,  the 
power  factor  is  not  nearly  so  favorable.  A  good  power 
factor  of  .85  to  .90  is  very  hard  to  obtain  in  motors  of 
moderate  size  and  speed  such  as  would  be  used  in  street 
railway  practice,  and  a  poor  power  factor  means  mischief. 

Take  for  example  a  power  factor  of  .75.  This  means 
that  a  third  more  current  must  be  generated  and  distrib- 
uted than  is  indicated  by  the  energy  and  the  voltage  of 
supply.  Hence  the  Caving  in  copper  effected  by  the  three 
phase  or  two  phase  three-wire  circuits  is  more  than  wiped 
out  at  once.  Moreover,  the  large  inductance  of  such  a 
circuit  involves  both  a  heavy  inductive  drop  and  a  very 
unfavorable  armature  reaction  in  the  generator.  Between 
these  and  the  extra  current  the  station  capacity  required 


ALTERNATING   MOTORS   FOR   RAILWAY   WORK.          2OI 


would  not  be  less  than  i  ^  times  that  needed  to  supply  the 
same  effective  energy  by  continuous  current. 

With  large  induction  motors  intended  for  rather  high 


Gerso  f? 


N 


St.Sa1vatore 

Cable  Railway 


Scale  1:25000 


Street  Railway  Journal 


FIG.  102. 

speed  it  is  practicable  to  keep  the  power  factor  well  up, 
high  enough  to  render  this  trouble  quite  insignificant. 

All  these  facts  point  to  the  desirability  of  developing 
polyphase  work  in  the  direction  of  fast  interurban  service 
and  heavy  long  distance  work  rather  than  toward  ordinary 
street  railway  equipment.  In  the  former  the  polyphase 


202     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

system  is  at  its  best,  its  many  good  features  are  thoroughly 
available  and  its  disadvantages  are  minimized. 

Nevertheless  the  abolition  of  the  commutator  is  so 
desirable  that  there  is  a  strong  tendency  to  work  polyphase 
apparatus  for  ordinary  purposes,  and  it  is  noteworthy  that 
the  first  polyphase  electric  road  to  be  put  in  operation 
belongs  distinctively  to  the  class  of  street  railways.  This 
very  important  piece  of  pioneering  work  was  carried  out 
in  1896  by  the  famous  firm  of  Brown,  Boveri  &  Company, 
at  Lugano,  Italy. 

I/ugano  is  a  fine  prosperous  town  situated  on  the  lake 
of  the  same  name  at  the  foot  of  the  Italian  Alps.  A  water- 
fall a  little  more  than  seven  miles  away  furnishes  power 
for  lighting  the  town,  and  is  now  utilized  for  the  railway 
as  well.  The  road  runs  for  the  most  part  along  the  lake 
front  on  each  side  of  the  town.  It  has  a  total  length  of  al- 
most exactly  three  miles,  and  its  general  situation  is  shown 
on  the  sketch  map  (Fig.  102).  There  are  only  moderate 
grades  of  about  three  per  cent  except  for  three  short 
pitches  of  six  per  cent. 

At  the  power  station  is  a  300  h.  p.,  horizontal  turbine 
direct  connected  by  a  flexible  coupling  to  a  150  k.  w.,  three 
phase  generator.  This  machine  is  of  the  inductor  station- 
ary armature  type  generally  advantageous  for  high  volt- 
ages and  is  wound  to  give  directly  5000  volts  between 
lines  at  40  ~.  The  exciter  armature  is  carried  directly  on 
the  main  shaft  so  that  the  generator  is  quite  self  contained. 
Its  speed  is  600  r.  p.  m. 

The  line  is  of  three  wires  each  about  No.  46.  &  S. 
gauge,  and  leads  at  present  to  a  single  transformer  station 
on  the  southern  edge  of  the  town  not  far  from  the  middle 
of  the  line.  The  three  phase  transformer  here  located  re- 
duces the  voltage  to  400  volts  which  is  the  working  press- 
ure between  the  conductors. 

The  conducting  system  consists  of  the  track  which  is 
thoroughly  bonded,  as  one  lead,  and  two  trolley  wires, 
each  about  No.  3  B.  &  S.  gauge.  Bracket  construction  is 
employed  and  the  two  trolley  wires  are  carried  side  by  side 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK.         203 

about  ten  inches  apart.  The  general  character  of  the  over- 
head structure  is  well  shown  in  Fig.  103.  The  current  is 
taken  off  as  there  shown  by  two  distinct  trolley  poles  set 
one  behind  the  other  about  forty  inches  apart.  This  separ- 
ation of  the  trolleys,  by  the  way,  has  been  found  to  be  the 
best  arrangement  when  using  a  double  trolley  continuous 
current  system.  The  trolleys  themselves  are  very  similar 
to  those  generally  used  in  this  country. 


FIG.  103. 

Four  motor  cars  are  now  in  use,  each  of  them  having  a 
twenty  horse  power  induction  motor  geared,  with  a  speed 
reduction  of  i  to  4  to  one  of  the  axles.  The  arrangement 
of  the  motor  and  its  suspension  from  the  truck  is  shown  in 
Fig.  104.  The  motor  itself  (Fig.  105)  is  of  the  iron  clad 
type  with  revolving  armature  furnished  with  three  collect- 
ing rings.  These  rings  permit  the  insertion  of  a  three-part 
resistance  in  the  secondary  circuit  for  the  purpose  of  speed 
regulation.  The  function  and  practical  effect  of  such  a 
rheostat  has  already  been  described.  In  this  case  it  has 


204  POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

been  found  to  permit  perfect  control  of  the  speed,  as  might 
be  anticipated,  but  with  poor  efficiency  at  low  speeds. 
The  normal  car  speed  is  between  nine  and  ten  miles  per 
hour.  The  starting  torque  of  the  motors  has  proved  to  be 
ample,  quite  sufficient  to  start  a  very  heavily  loaded  car 
from  rest  on  the  steepest  grade  on  the  line,  and  the  per- 


FIG.    104. 

formance  of  the  cars  has  been  on  the  whole  very  good. 
The  two  trolleys  perform  well,  and,  what  is  rather  extra- 
ordinary, the  heavy  alternating  currents  have  not  given 
so  much  trouble  as  might  be  expected  to  the  telephone 
system  of  the  town.  There  must  be  a  strong  element  of 


FIG.  105. 

good  luck  in  this  matter,  for  under  ordinary  circumstances 
induction  would  be  at  least  quite  perceptible,  although  the 
leakage  difficulties,  of  course,  are  practically  suppressed  as 
are  also  most  electrolytic  troubles. 

In  some  recent  two-motor  car  equipments  made  by 
Brown,  Boveri  &  Company,  a  quasi-series  connection  has 
been  employed  for  low  speeds,  the  induced  current  from 
one  motor  serving  as  the  inducing  current  in  the  other  as 


ALTERNATING   MOTORS   FOR   RAILWAY   WORK.         205 

in  the  ' '  concatenated  ' '  arrangement  already  mentioned. 
Although  such  devices  are,  as  indicated  already,  useful  in 
giving  a  fair  efficiency  at  low  speeds,  they  can  hardly  be 
regarded  as  the  full  equivalent  of  the  series  parallel  con- 
troller now  so  generally  and  successfully  used  with  con- 
tinuous current  motors. 

L,ast  July  a  notable  example  of  three-phase  railway 
work  was  put  into  operation  by  the  same  enterprising 
firm.  This  is  a  true  inter  urban  road  25  miles  long  between 


FIG.  106. 

the  towns  of  Burgdorf  and  Thun,  Switzerland,  running 
through  several  smaller  towns  on  the  way  and  connecting 
at  each  end  with  a  steam  line.  The  power  station  is  on 
the  Kander  River  at  Spies,  about  6  miles  beyond  Thun 
and  the  end  of  the  railway.  Here  are  installed  three 
phase  generators  direct  coupled  to  turbines.  From  the 
raising  transformers  current  is  delivered  at  16,000  volts, 
30  ro,  to  the  railway  transmission  line.  This  line  consists, 
of  three  5  m.  m.  (about  No.  4  B.  &  S.)  bare  wires  sup- 
ported on  porcelain  insulators.  The  line  follows  the  road 
in  general,  with  occasional  short  cuts  across  curves,  and 


206   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

feeds  14  transformer  stations  which  reduce  the  pressure  to 
750  volts  for  the  working  conductors. 

These  latter  are  of  8  m.  m.   (about  No.  o  B.  &  S.) 


wire  carried  on  cross  suspensions,  the  two  conductors 
being  about  43  ins.  apart  and  about  1 6  ft.  above  the  track. 
The  road  is  single  track  with  turnouts,  of  5  ft.  gauge, 
and  is  laid  with  a  plain  T  rail  weighing  about  73  Ibs.  per 
yard,  on  steel  ties  placed  a  little  over  30  ins.  between 
centers.  The  maximum  grade  is  2.5  per  cent. 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK.         207 


<$> 


208     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

The  electrical  equipment  of  the  road  consists  of  two 
locomotives,  each  driven  by  two  150  h.  p.  motors,  and  six 
motor  cars  each  with  four  55  h.  p.  motors.  Current  is 
taken  from  the  working  conductors  by  four  bow  trolleys 
in  pairs  side  by  side  at  each  end  of  the  car.  Fig.  106  gives 
a  good  idea  of  the  motor  car,  trolleys  and  working  con- 
ductors. The  motors  are  arranged  much  as  is  usual  in 
four  motor  car  equipments,  two  on  each  truck,  single 
geared  to  the  axles.  Their  full  load  speed  is  586  r.  p.  m. 
and  they  are  controlled  by  rheostatic  resistances  in  the 
revolving  secondaries.  Fig.  107  shows  the  general  ar- 
rangement of  the  trucks.  The  wheels  are  40  ins.  in  diam- 
eter corresponding  to  railway  rather  than  tramway  condi- 
tions. In  fact  the  whole  line  is  worked  on  the  block 
system  and  follows  railway  practice  throughout,  the  cars 
being  equipped  with  air  brakes  and  run  in  short  trains  as 
in  ordinary  suburban  work,  at  a  normal  full  speed  of  22.5 
m.  p.  h.  "The  brakes  are  worked  by  an  automatic  motor 
compressor  and  the  cars  are  lighted  and  heated  electric- 
ally. In  general  the  whole  equipment  is  that  of  a  thor- 
oughly up-to-date  heavy  interurban  electric  road,  developed 
for  polyphase  transmission.  Fig.  108  gives  the  electrical 
diagram  of  one  of  the  motor  cars  showing  the  various 
connections.  It  should  be  noted  that  the  rheostats  are 
worked  by  a  rod  from  the  controller  instead  of  being  elec- 
trically connected  to  it.  The  motor  cars  accommodate  68 
passengers  and  weigh  fully  equipped  32  tons.  The  loco- 
motives are  intended  largely  for  freight  service  and  have 
a  capacity  sufficient  to  haul  easily  a  100  ton  train  up  the 
2.5  per  cent  grade  at  a  little  better  than  11  m.  p.  h.  They 
have,  however,  change  gearing  to  enable  them  to  be 
speeded  up  for  passenger  traffic  when  needful. 

Fig.  109  shows  one  of  the  fourteen  transformer  sta- 
tions. Each  of  these  consists  of  a  450  k.  w.  three-phase 
oil  transformer  in  a  sort  of  gigantic  metallic  sentry  box 
on  a  concrete  foundation.  Above  and  in  the  rear  are  the 
cut-outs,  fuse  boxes  and  lightning  arresters.  The  trans- 
former stations  are  located  close  to  the  way  stations,  and 


ALTERNATING   MOTORS    FOR   RAILWAY   WORK. 


209 


are  under  the  charge  of  the  station  masters.  The  whole 
system  is  a  practical  demonstation  of  the  applicability  of 
the  three-phase  system  to  the  working  of  interurban  lines 
on  a  large  scale.  The  most  startling  thing  about  the  road 
is  the  singularly  small  amount  of  copper  required.  Aside 
from  the  high  tension  line  there  is  no  feeding  system,  all 


FIG.  109. 

the  current  being  distributed  over  the  working  conductors. 
The  total  coppe'r  in  the  system  is  only  about  145,000  Ibs. 
worth  at  the  basic  price  of  15  cts.,  $21,750,  less  than  $1000 
per  mile  of  line.  This  for  a  system  designed  for  motors 
of  more  than  1800  h.  p.  total  capacity  is  sufficiently  re- 
markable to  afford  considerable  food  for  contemplation. 
American  engineers  have  fought  shy  of  undertaking  this 
line  of  work,  preferring  the  easier  but  more  costly  and 


210    POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

less  efficient  method  of  transmitting  to  rotary  converters. 
In  the  logical  development  of  railway  work,  however,  the 
polyphase  motor  certainly  has  a  legitimate  place  and  it  is 
unwise  to  make  a  fetish  of  uniformity  to  the  extent  of 
barring  the  way  to  progress. 

The  problem  is  being  worked  out  for  us  abroad  in 
roads  like  the  one  just  described,  and  in  due  time  we  may 
profit  by  it  as  we  profited  nearly  a  decade  ago  by  the 
I,auffen- Frankfort  experiment  in  polyphase  transmission. 

IV.  Motors  of  the  asynchronous  type  working  on  a 
monophase  circuit  are  not  as  yet  far  enough  developed  to 
be  immediately  available  for  railway  purposes,  although 
they  have  come  abroad  into  considerable  use  for  general 
motor  work  in  connection  with  lighting  service. 

They  may  be  divided  into  two  classes,  rather  distinct 
from  each  other  in  method  of  operation,  although  closely 
similar  to  each  other  in  principle  and  in  practical  qualities. 

First  may  be  mentioned  those  motors  which  are  oper- 
ated as  true  polyphase  motors  by  derived  polyphase  cur- 
rents obtained  by  splitting  up  a  monophase  current.  In 
this  case  the  actual  motor  is  a  true  polyphase  machine  with 
all  the  properties  thereto  belonging,  and  the  real  novelty 
of  the  system  lies  in  the  special  methods  of  transformation 
adopted  in  breaking  up  an  ordinary  alternating  current 
into  symmetrical  components. 

Systems  of  this  sort  have  been  brought  forward  in  this 
country  by  C.  S.  Bradley  and  abroad  by  M.  Desire  Korda. 
They  are  somewhat  complicated,  but  are  nevertheless 
operative,  and  may  find  a  field  even  in  electric  traction, 
particularly  in  special  problems  in  railroading. 

The  apparatus  of  Mr.  Bradley  is  shown  in  diagram  in 
Fig.  no.  The  process  employed  consists  essentially  of 
two  operations — the  splitting  up  of  the  original  current 
into  two  components,  differing  in  phase  by  90  degs. ,  and, 
second,  the  combination  of  these  to  obtain  a  three  phase 
resultant  system.  In  the  diagram,  A  is  the  generator, 
B  one  section  of  the  transformer  primary  system,  D  a 
condenser  which  acts  in  conjunction  with  the  inductance 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK.        211 

of  the  compound  section  of  the  transformer  system  to  pro- 
duce the  requisite  90  deg.  phase  difference,  n  and  /,  the 
parts  of  the  compound  transformer,  and  g  h  i  j  k  the 
segments  of  the  secondary  windings.  Once  given  the  two 
phase  current,  the  shifting  over  to  three  phase  is  easy. 
The  coii,  z,  furnishes  one  phase,  the  resultant  of  g  and  k  a 
second,  and  the  resultant  of  h  and/  the  third,  all  of  which 
are  connected  in  the  ordinary  way  to  the  motor,  M.  The 
result  of  this  very  ingenious  combination  is  a  very  close 


FIG.  no. 

approximation  to  a  true  three  phase  relation  throughout  a 
considerable  range  of  load,  both  in  starting  and  running. 
The  use  of  three  resultant  phases  tends  to  preserve  a  more 
uniform  phase  relation  than  would  be  obtained  by  utilizing 
the  original  two  derived  phases. 

The  employment  of  a  condenser,  while  it  adds  to  the 
complication,  tends  to  annul  the  inductance  of  the  main 
circuit.  At  all  events  it  can  be  made  to  give  a  very  high 
power  factor,  better  than  that  given  by  ordinary  poly- 
phase motors. 

On  the  other  hand,  the  condenser  is  an  element  of 
weakness  in  that  it  is  of  somewhat  uncertain  life,  and  un- 
less exposed  to  high  voltage  and  used  at  rather  high  fre- 
quency, is  both  bulky  and  expensive.  Its  use  involves 


212   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

difficulties  in  the  way  of  maintenance  that,  while  probably 
surmountable,  are  serious  in  its  application  to  railway  con- 
ditions. 

M.  Korda's  device  dispenses  with  the  condenser  and 
initially  splits  up  the  primary  monophase  current  into  two 
components  60  degs.  apart  by  inductance  alone  and  re- 
combines  these  so  as  to  give  three  phase  resultants.  It 
gives  a  somewhat  less  stable  phase  relation  and  power  fac- 
tor than  the  method  just  described  employing  a  con- 
denser. 

Second  in  the  list  of  motors  for  monophase  circuits 
comes  that  class  which  employs  a  split  phase  current  at 
starting  to  obtain  a  simultaneous  transformer  and  motor 
action,  but  in  running  is  purely  monophase.  Motors  of 
this  kind  have  been  considerably  developed  abroad,  but  are 
only  used  tentatively  in  this  country.  As  at  present  made 
they  all  start  either  with  very  poor  torque,  or  if  with  better 
torque  demand  an  enormous  starting  current,  which  lags 
badly.  When  once  up  to  speed,  however,  they  perform 
wrell  although  never  with  as  high  output  as  a  polyphase 
motor  of  the  same  dimensions  and  efficiency.  There  are  a 
large  number  of  wrays  of  getting  the  phase  difference  at 
starting,  some  of  them  requiring  modifications  of  the  motor 
structure,  others  merely  special  connections.  A  consider- 
able variety  of  phase  splitting  devices  were  devised  by 
Tesla  as  corollaries  to  his  pioneer  polyphase  work  and  di- 
vers others  have  been  added  to  the  list.  Variations  of  cap- 
acity and  inductance  in  branches  of  the  main  circuit  exter- 
nal to  the  motor  are  most  often  used. 

In  construction  and  appearance  these  monophase 
motors  are  closely  similar  to  the  polyphase  ones  already 
described.  Indeed  most  polyphase  motors  can  be  worked 
as  monophase  motors  with  very  trifling  changes.  When 
carefully  designed,  these  machines  give  a  high  efficiency 
and  a  high  power  factor  when  once  at  speed.  Fig.  in 
gives  the  curves  of  efficiency  and  power  factor  for  a  fifteen 
horse  power,  Brown,  monophase,  asynchronous  motor  de- 
signed for  a  speed  of  about  850  r.  p.  m.  at  40^. 


ALTERNATING   MOTORS   FOR   RAILWAY   WORK.        213 

These  results  are  nearly  as  good  as  can  be  obtained 
from  a  polyphase  motor  of  similar  output,  but  since  most 
of  these  monophase  motors  are  built  with  exceedingly 
small  clearance  for  the  armature,  down  to  less  than  ^  in., 
there  is  little  likelihood  of  approximating  closely  the  fig- 
ures just  given  with  a  motor  fit  for  railway  work.  Nor  is 
it  possible  to  get  effective  speed  regulation  in  monophase 
motors  by  a  resistance  in  the  secondary  or  any  other  simple 
means. 

Summing  up  the  present  state  of  the  art,  we  find  that 
kfre  only  alternating  motors  yet  constructed,  of  properties 


100 


70 


10 
H.  P.  out  put 


FIG.    III. 


Street  Ry.Journal 


immediately  suitable  for  railway  service,  are  the  polyphase 
induction  motors,  which  while  often  weak  in  power  factor, 
are  of  sufficient  efficiency  and  general  excellence  to  replace 
existing  continuous  current  motors.  It  is  certain  too,  that 
the  lag  factor  trouble  can  be  overcome  by  careful  design 
particularly  if  the  frequency  is  kept  low,  say,  30^  to  40^. 
The  synchronous  motors,  both  monophase  and  poly- 
phase, have  excellent  properties  when  up  to  speed,  but  do 
not  start  will  except  at  the  cost  of  considerable  complica- 
tion. Tjie  commutating  start  appears  to  give  the  best 
torque,  but  this  is  not  comparable  with  the  best  that 
can  be  done  by  polyphase  induction  motors.  The  whole 


214   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

class  are  liable  to  poor  power  factors  when  starting,  though 
when  running  the  power  factors  are  uniformly  high. 

The  induction  motors  for  monophase  circuits  are  still 
in  an  early  stage  of  development  as  regards  application  to 
such  severe  service  as  is  necessary  on  electric  railways. 
The  most  promising  of  them  are  those  supplied  with  de- 
rived polyphase  currents  even  if  this  advantage  involves 
the  use  of  condensers,  since  they  can  be  made  to  give  high 
starting  torque  and  a  good  power  factor.  The  starting  de- 
vices applied  to  all  existing  strictly  monophase  motors  are 
entirely  insufficient  for  railway  purposes  unless  a  clutch 
connection  is  used  in  which  rather  unmechanical  case  syn- 
chronous motors  would  be  generally  preferable. 

With  derived  polyphase  circuits,  at  least  for  starting,  it 
is,  in  the  author's  opinion,  entirely  practicable  to  produce 
even  now  a  motor  for  monophase  circuits  entirely  capable 
of  doing  certain  railway  work  successfully. 

It  does  not  follow  from  this  that  all  classes  of  electric 
railway  work  can  now,  or  ever,  be  accomplished  best  by 
the  use  of  alternating  motors  of  any  sort.  But  the  same 
logic  of  circumstances  that  has  brought  alternating  sys- 
tems into  increasing  use  for  lighting  and  general  power 
purposes  applies  to  railway  work  with  ominous  force.  It 
is  altogether  probable  that  for  a  vast  amount  of  strictly 
street  railway  work  the  continuous  current  motor  is  here 
to  stay.  In  its  present  state  of  development  it  is,  at  least 
as  a  motor,  as  good  as  any  alternating  current  motor  is 
likely  to  be.  But  the  question  of  voltage  presses  hard, 
and  as  the  distances  to  be  reached  continually  grow  the 
time  comes  when  a  distribution  that  can  be  used  for  con- 
tinuous current  motors  becomes  outrageously  costly  in  ma- 
terial or  in  loss  of  energy.  The  economic  value  of  alter- 
nating motors  depends  on  their  adaptation  to  a  very 
economical  method  of  distribution.  In  many  cases  they 
not  only  meet  this  condition,  but  can  be  applied  with  ad- 
vantage irrespective  of  the  distribution  system. 

For  urban  work  they  possess  few  intrinsic  advantages 
over  continuous  current  motors.  For  much  interurban 


ALTERNATING   MOTORS   FOR   RAILWAY  WORK.        215 

and  long  distance  work  they  are  not  only  important  as  a 
part  of  the  distribution,  but  have  some  material  points  of 
superiority.  In  such  work,  with  infrequent  stops  at  stated 
intervals,  their  tendency  to  run  at  a  uniform  speed  irres- 
pective of  grade  and  load  must  be  very  useful  in  main- 
taining the  running  schedule.  The  maintenance  of  speed 
in  spite  of  moderate  variations  in  voltage  is  also  useful  in 
working  long  feeders  at  variable  load,  and  the  possibility 
of  working  at  high  voltages  greatly  simplifies  the  problem 
of  drawing  large  amounts  of  energy  from  the  working 
conductors. 

The  alternating  motor  is  then  fortunately  best  adapted 
to  that  class  of  work  in  which  the  exigencies  of  distribu- 
tion make  it  most  necessary.  In  high  speed  and  long  dis- 
tance work  lies  its  chief  strength,  and  when  this  kind  of 
railroading  is  attempted  in  earnest  it  is  quite  safe  to  say 
that  alternating  motors  will  be  used. 

For  light  railways  running  considerable  distances 
across  country  also,  the  alternating  motor  is  peculiarly 
adapted. 

In  no  way  can  the  importance  of  this  branch  of  work 
be  exhibited  more  forcibly  than  by  computing  the  initial 
and  operating  expense  of  a  road  under  assumed  condi- 
tions; first,  utilizing  continuous  currents;  second,  employing 
transmission  to  substations  with  rotary  transformers,  and 
finally,  using  an  alternating  distribution  with  alternating 
motors.  It  is,  of  course,  quite  impossible  to  select  a  case 
that  will  be  exactly  equally  fair  to  all  three  methods,  but 
we  can,  perhaps,  approximate  to  a  fair  general  case. 

Let  us  assume  an  electric  road  thirty  miles  in  length 
running  through  a  series  of  villages  with  two  cities  of 
moderate  size  as  termini.  For  simplicity  we  will  assume 
that  the  cost  of  fuel  and  labor  is  uniform  throughout  the 
line  so  that  the  location  of  the  station  is  uninfluenced  to 
any  extent  by  local  conditions.  The  train  service  we  will 
assume  to  be  conducted  on  a  twenty  minute  headway,  the 
actual  running  time  being  two  hours,  including  stops. 
This  would  keep  twelve  cars  in  service.  We  will  also  as- 


2l6    POWER    DISTRIBUTION    FOR   ELECTRIC    RAILROADS. 

sume  the  grades  to  be  moderate  so  that  the  power  required 
would  be  fairly  uniform  throughout  the  line.  The  cars 
stop  at  fixed  points  only,  with  good  opportunity  for  clear 
running  over  a  large  part  of  the  system.  With  ordinary 
conditions  of  load  the  use  of  two  twenty-five  horse  power 
or  thirty  horse  power  motors  per  car  would  be  sufficient 
and  the  normal  current  demanded  should  not  exceed  fifty 
amperes  per  car  or  one  hundred  amperes  per  car,  at  500 
volts  as  a  maximum  for  the  system.  The  total  output  to 
be  delivered  to  the  cars  may  then  be  taken  at  300  k.  w. 
average  and  600  k.  w.  maximum. 

For  such  a  line  as  this  four  methods  of  supply  would 
be  worth  investigation:  I,  direct  supply  from  two  sym- 
metrically placed  stations;  II,  supply  from  a  single  station 
with  boosters;  III,  supply  from  one  station  with  a  rotary 
transformer  substation;  IV,  supply  from  a  single  station  by 
alternating  currents  and  static  transformers.  For  sim- 
plicity, we  will  assume  the  cost  of  track  and  overhead 
structure  to  be  the  same  for  all  four.  So,  in  fact,  it  would 
be  for  the  first  three  methods,  and  the  extra  working  volt- 
age readily  obtained  with  the  alternating  system  at  least 
compensates  for  lagging  current  in  the  trolley  wire  or  the 
extra  expense  of  stringing  and  maintaining  two  trolley 
wires,  if  the  polyphase  system  is  used.  We  will  compare 
the  systems  on  the  basis  of  the  same  loss  of  energy 
reckoned  from  generator  to  motor,  since  the  efficiency 
of  generators  and  motor  is  substantially  the  same  through- 
out, and  for  simplicity  will  not  figure  out  close  details  of 
distribution,  but  reckon  the  copper  required  in  the  simplest 
possible  manner.  The  permissible  loss  of  energy  from  gen- 
erator to  working  conductor,  we  will  take  as  fifteen  per 
cent  at  maximum  load,  allowing  five  per  cent  loss  in  the 
trolley  wire.  We  have  already  seen  that  if  maximum  load 
is  taken  care  of ,  the  average  load  will  look  out  for  itself . 

In  supplying  current  from  two  separate  power  houses 
these  would  naturally  be  placed  15  miles  apart  and  7^ 
miles  from  each  end  of  the  line.  Each  power  house 
would  then  feed  half  the  line,  7^  miles  on  each  side  of  its 


ALTERNATING   MOTORS    FOR   RAILWAY   WORK.        217 

location.  The  average  distance  of  transmission  would  then 
be  3^  miles,  quite  nearly  17,000  ft. 

The  maximum  voltage  for  standard  generators  may  be 
taken  as  about  600,  giving  with  fifteen  percent  loss  510 
volts  at  the  motors.  Each  station  would  have  to  be  able 
to  deliver  600  amperes  at  a  distance  of  17,000  ft.,  with  a 
less  of  ninety  volts.  Falling  back  on  our  stock  formula 

w  =  42X600X289  =  80)920  lbs> 

90 

At  current  prices  (fifteen  cents  per  pound)  this  would 
mean  the  expenditure  of  $24,276  for  feeder  copper  for  the 
two  stations.  The  annual  output  for  both  stations  would 
be  about  2,000,000  k.  w.  hours. 

The  operating  expense  of  two  stations  each  of  300 
k.  w.  maximum  output  would,  of  course,  be  decidedly 
more  than  if  the  output  were  concentrated  in  a  single 
station.  The  extra  expense  due  to  this  cause  can  be  esti- 
mated with  fair  accuracy.  With  coal  at  about  $3  per 
ton  it  would  probably  amount  to  0.25  cents  per  kilowatt 
hour,  the  difference  between,  say,  1.5  cents  per  kilowatt 
hour  with  a  single  station  and  about  i .  75  cents  with  the 
two  stations.  The  total  extra  expense  would  be  then 
about  $5000  per  year. 

With  a  booster  system  the  principal  gain  would  be 
the  ready  use  of  the  extra  working  voltage  on  the  line. 
The  motors  could  with  advantage  be  run  at  575  to  600 
volts  giving,  say,  700  volts  for  transmission.  The  dis- 
tance of  transmission  would,  however,  be  doubled,  as  the 
best  situation  for  the  station  would  be  the  center  of  the 
line.  Taking  now  the  average  distance  as  34,000  ft.  the 
current,  reduced  by  the  extra  voltage,  as  525  and  the  per- 
missible volts  drop  as  105,  we  have  as  before 

w  =  42X525X11,56  =  242>76o  lbs< 

105 

for  the  transmission  in  each  direction,  giving  a  total  of 
double  this  amount  costing  at  15  cents  per  pound  $72,628. 
The  boosting  apparatus  would  probably  add  $2500  to  the 
cost  of  the  station,  and  the  cost  per  kilowatt  hour  generated 


2l8    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

would  be  as  above,  about  1.5  cents  for  2,000,000  k.  w.  h, 
per  year. 

Now  coming  to  the  transmission  systems  proper,  with 
a  substation  and  rotary  transformers  the  cost  of  the  funda- 
mental station,  with  double-ended  generators  would  be 
about  the  same  as  for  an  ordinary  continuous  station.  For 
the  transmission  there  must  be  added  a  set  of  raising  trans- 
formers of  about  300  k.  w.  costing,  say,  $10  per  kilowatt, 
and  extra  switchboards  and  subsidiary  apparatus  amounting 
to,  say,  $1000.  The  line  will  have  the  advantage  of  high 
voltage,  but  the  drop  will  have  to  be  small  since  the  loss  in 
transformers  and  the  rotary  transformer  must  come  out  of 
the  fifteen  per  cent  allowed  as  total.  With  the  best  efficien- 
cies that  can  be  expected  from  these  the  line  loss  must 
not  exceed  four  per  cent.  The  voltage  of  transmission 
may  be  taken  as  10,000,  hence  the  drop  would  be  400  volts. 
The  copper  must,  of  course,  be  figured  as  a  complete  metallic 
circuit,  and  the  formula  will  become 


in  this  case  the  current  may  be  taken  as  thirty-five  to  make 
allowance  for  residual  lag  and  Lm  is  about  sixty-eight. 
We  get,  therefore,  for  the  transmission  line 

w=  44X3X35X  H56X4  81b 

400 

in  all  costing,  at  15  cents  per  pound,  $8012.  At  the  sub- 
station there  will  be  switchboards,  transformers  and 
rotary  transformers  for  300  k.  w.  ,  which  with  the  house 
may  be  lumped  at  $10,000. 

Beyond  these  costs  of  transmission  is  the  distribution 
system  of  feeders,  which  will  cost  the  same  as  in  Case  I, 
together  with  the  maintenance  and  depreciation  of  the 
transmission  plant  and  labor  at  the  substation,  in  all,  say, 
$4000  per  year.  And  even  after  this  comes  the  fact  that 
although  the  voltage  on  the  working  lines  can  be  bold 
within  the  fifteen  per  cent  limit  of  loss,  we  still  have  ihe 
energy  loss  in  the  distribution  system  of  feeders. 

With  alternating  motors  the  case  is  very  different.. 


ALTERNATING   MOTORS   FOR   RAILWAY   WORK.        219 

The  station  generating  apparatus  has  the  same  cost  as  be- 
fore. The  reducing  transformers  may  be  taken  at  $4000. 
The  whole  feeder  system  would  be  at  high  tension,  and 
there  would  be  no  need  for  raising  transformers,  since  the 
fairly  large  station  generators  could  well  give  5000  volts 
and  be  overcompounded  for,  say,  ten  per  cent  loss  in  the 
line.  The  cost  of  machines  for  such  voltage  might  be 
slightly  higher,  perhaps  $1000  on  the  plant.  A  like 
amount  should  be  added  for  high  tension  switchboard  and 
extra  appliances.  Now  the  total  energy  in  this  case  is 
transmitted  an  average  distance  of  34,000  ft.,  as  in  the 
booster  distribution.  Using  the  same  formula  as  in  the 
preceding  case  we  have,  allowing  ten  per  cent  line  loss, 
and  fifteen  per  cent  extra  current  to  compensate  for  lag, 

44X3X  138X1156 
W  =  ~  ~^o~~~          "  =  42>°?8  Ibs. 

of  copper,  costing  $6312.     It  is  but  fair  at  present  to  as- 
sume an  extra  cost  of  fifty  per  cent  for  the  car  equipments, 
say,  $500  per  car  for  fifteen  cars,  in  all  $7500. 
We  may  now  gather  these  data  as  follows  : 


Case. 

Cost  of 
copper. 

Cost  of 
Extra 
apparatus. 

Cost  of 
2,000,000 
kwh. 

10  %  on 
copper. 

10  %  on 
extra 
app. 

Extra 
labor  for 
working. 

Sum  of 
these 
anuual 
charges. 

I. 

$24) 

276 

$35,ooo 

$*> 

427 

$37,427 

II. 

72, 

628 

$2 

,500 

30,000 

7, 

262 

$ 

250 

37,512 

III. 

32, 

288 

14 

,OOO 

30,000 

3> 

228 

I 

,400 

$2,500 

37,128 

IV. 

6, 

312 

13 

,500 

30,000 

631 

I 

,350 

31,981 

These  figures  speak  for  themselves.  In  reality  III  is, 
under  the  assigned  conditions,  decidedly  inferior  to  the 
others  in  efficiency,  as  already  indicated.  It  can  only  be 
used  economically  under  rather  rare  conditions,  and  then 
only  in  default  of  a  proper  alternating  motor  system.  I 
and  II  are  almost  exactly  equivalent,  and  very  small  differ- 
ences in  cost  of  power  generation  would  throw  the  advan- 
tage one  way  or  the  other.  IV  is  easily  the  best,  and 
would  still  hold  its  position  of  superiority  in  the  face  of  a 
considerably  larger  allowance  for  lagging  current  tljan  that 
here  made.  With  a  smaller  permissible  loss  of  energy  than 
fifteen  per  cent,  the  booster  system  would  drop  rapidly  to 


220   POWER   DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 

third  place  in  desirability,  and  IV  would  have  even  greater 
advantage  than  at  present,  while  III  would  be  out  of  the 
question.  Any  increase  in  the  price  of  copper  or  decrease 
in  the  cost  of  apparatus  would  give  a  still  further  advant- 
age to  the  alternating  motor  system.  It  should  be  noted 
that  the  tabulated  figures  do  not  in  any  case  include  the 
working  conductors. 

At  all  distances  and  losses  a  good  alternating  system 
would  be  in  the  front  rank,  and  excepting  at  very  moderate 
distances,  would  easily  lead.  One  fact,  however,  must  be 
remembered.  An  alternating  current  does  not  penetrate 
far  into  the  substance  of  an  iron  conductor,  hence  in  using 
an  alternating  system  the  rails  cannot  be  counted  on  for 
their  full  conductivity.  This  would  be  very  serious  even 
at  25  no  if  it  were  not  that  the  magnetizing  force  due  to 
the  current  in  the  rails  would  under  ordinary  circum- 
stances be  so  low  that  the  permeability  of  the  steel  would 
be  small,  not  over  200  to  300.  At  25  *\/  the  equivalent 
conductivity  of  rails  of  the  usual  sections-  cannot  safely  be 
taken  at  over  0.5  the  usual  value,  perhaps  as  low  as  0.3. 
Fortunately,  in  the  interurbaii  and  long  distance  lines  for 
which  alternating  motors  are  most  .  needed,  the  current 
density  in  the  rails  is  likely  to  be  so  low  that  the  permea- 
bility is  kept  down  and  the  rails  are  still  fairly  good  con- 
ductors. 


CHAPTER  VIII. 

INTERURBAN   AND    CROSS    COUNTRY   WORK. 

The  most  important  class  of  electric  roads  at  present 
is  that  composed  of  tramways  that  have  outgrown  and 
reached  beyond  their  urban  starting  points  and  serve  to 
interlink  cities  and  villages.  These  lines  are  important 
and  interesting  to  the  engineer,  since  they  are  often  sub- 
ject to  unusual  conditions  and  require  special  treatment, 
and  they  are  of  immense  value  and  importance  to  the  pub- 
lic, because  they  tend  to  break  down  the  industrial  barriers 
that  have  been  artificially  established  between  city  and 
country,  and  give  to  both  some  of  the  advantages  now 
peculiar  to  each. 

There  is  nothing  in  the  nation's  growth  more  menac- 
ing to  good  government  and  the  healthy  growth  of  industry 
than  the  rapid  concentration  of  population  and  enterprise 
at  a  small  number  of  overcrowded  spots. 

The  opening  of  easy  channels  of  communication 
through  the  country  at  large,  increases  enormously  the 
areas  available  for  profitable  manufacture  and  decent  habi- 
tation. Much  has  already  been  accomplished  by  the  in- 
terurban  and  suburban  electric  railway  systems  already 
installed,  and  much  more  can  be  done  by  the  extension 
of  these  lines  and  the  building  of  new  lines  through  regions 
that  are  now  isolated. 

Fig.  112,  showing  the  connected  system ,  of  which  Boston 
is  the  center,  gives  a  vivid  idea  of  the  extent  of  country 
covered  and  the  thoroughness  with  which  the  work  of  in- 
terconnection is  done  in  certain  regions.  Still,  large  dis- 
tricts are  left  untouched,  giving  ample  room  for  further 
extensions:  The  districts  already  interlaced,  however, 
have  an  aggregate  population  of  very  nearly  1,250,000  in- 


222    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

habitants.  And  all  this,  with  few  exceptions,  is  the  result 
of  extension  of  strictly  urban  systems  and  not  of  independ- 
ent effort  at  new  avenues  of  intercommunication. 

This  character  of  growth  is  attested  by  the  fact  that  of 


the  entire  network  only  the  road  from  Lowell  to  Nashua, 
N.  H.,  and  the  isolated  Nantasket  Beach  road,  differ  in 
engineering  features  from  the  general  practice  on  purely 
urban  roads.  Practically  all  the  work  is  done  in  the  ordi- 
nary way  at  about  500  volts.  Of  course,  the  tout  ensemble 
is  a  shocking  example  of  inefficient  and  costly  distribu- 


INTERURBAN  AND  CROSS  COUNTRY  WORK.     22$ 

tion — the  necessary  result,  however,  of  its  manner  oi 
growth.  Some  of  the  component  systems,  of  course,  are 
beautifully  designed. 

Most  existing  roads  of  the  interurban  class  have  in 
similar  fashion  been  the  result  of  extensions,  but  recently 
there  has  been  a  tendency  toward  systems  intended  delib- 
erately for  interurban  work,  and  designed  with  this  in 
view.  Such  is  the  system  about  Cleveland,  O.,  described 
in  a  former  chapter,  the  recently  opened  line  between  L,os 
Angeles  and  Santa  Monica,  Cal. ,  and  divers  others.  These 
lines  are  rapidly  increasing  in  numbers  and  form  the  con- 
necting link  between  street  railways  with  thefr  suburban 
extensions  on  the  one  hand,  and  electric  systems  replacing 
;steam  railroads  on  the  other. 

The  distinction  between  these  classes  is  somewhat  ar^ 
tificial,  but  none  the  less  real.  We  shall  consider  only 
those  roads  that  are  prepared  to  operate  capacious  trains 
at  speeds  of  thirty  miles  per  hour  and  upwards  as  really 
entering  upon  the  functions  of  ordinary  railroads.  The 
strictly  interurban  roads  have  a  function  of  their  own,  and 
a  most  important  one,  in  linking  together  urban  systems 
and  opening  up  direct  service  between  points  previously 
connected  very  indirectly. 

A  glance  at  Fig.  112  will  show  that  the  latter  f  unction 
is  even  now  very  imperfectly  fulfilled.  There  are  still 
left  great  areas  in  which  there  is  no  intercommunication 
except  by  paying  a  double  tariff  into  and  out  of  one  of  the 
larger  cities. 

The  cross  country  roads,  as  yet  but  little  used  in 
this  country  are  destined  to  play  a  very  important  part  in  the 
development  of  our  country.  They  should  serve  as  feeders 
both  for  steam  roads  and  interurban  electric  roads,  form- 
ing the  capillaries,  as  it  were,  of  the  industrial  circulation. 
They  are  naturally  allied  to  interurban  systems,  but  owing 
to  the  necessity  for  cheap  construction  and  the  compara- 
tive unimportance  of  high  speed,  must  be  separated  from 
them  in  engineering  details  and  particularly  in  equipment. 

The  interurban  road  proper  differs  from  the  ordinary 


224   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

street  railway  in  several  very  important  particulars.  Firsts 
the  speed  is  on  the  average  very  much  higher;  second,  the 
stops  are  relatively  much  less  frequent;  third,  the  average 
distance  between  generator  and  motors  is  far  greater;  and 
fourth,  the  average  power  per  car  is  considerably  more  in 
amount. 

As  regards  the  first  count,  the  actual  speed  on  all  elec- 
tric roads  is  apt  to  be  overestimated.  Most  cars  on  street 
railways  have  an  average  speed,  including  stops,  nearer  five 
miles  an  hour  than  ten,  as  can  readily  be  figured  from  the 
hours  of  running  and  the  average  daily  mileage.  Now 


FIG.  113. 

for  runs  between  town  and  town  much  greater  speed  than 
this  is  desirable  and  can  be  readily  reached  in  the  absence 
of  traffic  obstructions. 

The  interurban  line  should  be  able  to  make  at  least 
double  the  average  speed  of  the  street  railway  proper,  and 
this  means  from  twelve  to  eighteen  miles  per  hour  includ- 
ing ordinary  stops.  The  maximum  speed  corresponding 
to  this  is  likely  to  be  from  twenty  to  thirty  miles  per  hour, 
seldom,  however,  the  latter  figure.  The  general  running 
speed  is  likely  to  be  between  fifteen  and  twenty  miles  per 
hour,  seldom  the  latter  figure. 

These  speeds  call  at  once  for  modifications  of  standard 
cars  and  trucks.  Under  such  conditions  the  common  single 
truck  is  positively  unsafe  on  ordinary  track,  and  recourse 


INTKRURBAN  AND  CROSS  COUNTRY  WORK. 


225 


must  be  taken  to  double  truck  cars.  The  importance  of 
this  has  been  emphasized  by  several  serious  accidents  from 
attempting  high  speeds  with  single  trucks. 

So  in  the  natural  course  of  evolution  a  fine  type  of 
double  truck  car,  similar  to  that  used  on  many  large  urban 
systems  has  come  to  be  used  for  most  interurban  service. 
Such  a  car  is  well  shown  in  Fig.  113.  It  is,  save  in  size, 
closely  similar  to  an  ordinary  railroad  car,  having  the  same 


FIG.    114. 

general  interior  arrangement.  It  is  forty  feet  long,  ves- 
tibuled  at  one  end,  and  is  provided  with  special  air 
brakes. 

Another  recent  interurban  car  partly  open  and  partly 
closed  (a  favorite  construction  on  the  Pacific  Coast)  is 
shown  in  Fig.  114..  This  is  rather  lighter  and  five  feet 
shorter  than  Fig.  113,  and  like  it  is  provided  with  air 
brakes. 

At  interurban  speeds,  electric  or  air  brakes  are  almost 
a  necessity  and  on  the  later  roads  are  quite  generally  pro- 
vided. As  .a  rule  too,  the  wheels  are  larger  than  the 
thirty-three  inch  size  now  standard  on  most  street  rail- 
ways, thirty-six  and  forty-two  inch  wheels  not  being  in- 


•226   POWER   DISTRIBUTION   FOR   ELECTRIC    RAILROADS. 

frequent.  These  sizes  give  more  room  for  the  larger 
motors  required  and  are  better  adapted  for  the  cars. 

As  to  track,  careful  laying  and  good  ballasting  are 
the  essential  points.  The  rails  themselves  are  what  would 
be  used  for  a  light  steam  railroad,  forty  to  sixty  pound  T 
being  the  rule,  although  at  the  termini  the  usual  girder 
rails  often  have  to  be  employed.  It  should  be  remembered 
that  a  city  track  gets  far  more  wear  and  tear  than  the 
average  interurban  track  and  must  be,  accordingly,  even 
more  substantial. 

The  rather  infrequent  stops  in  interurban  work  pro- 
duce on  the  whole  a  tendency  toward  uniform  distribution 
of  load  that  operates  favorably  on  the  necessary  distribu- 
tion of  power.  The  service  is  less  liable  to  blockades,  it 
is  easier  to  hold  to  a  regular  schedule  and  there  is  less  of 
the  troublesome  shifting  of  the  load,  than  in  street  railway 
practice.  Consequently  it  is  somewhat  easier  to  plan  the 
feeder  system. 

On  the  other  hand,  the  average  distance  to  which 
power  has  to  be  transmitted  is  considerable,  so  that  the 
aggregate  amount  of  feeder  copper  is  great,  and  it  is  ag- 
gravated by  the  frequent  attempts  to  transmit  power  un- 
reasonably long  distances  at  500  volts  to  avoid  distributed 
stations  or  other  appropriate  methods. 

The  absolute  amount  of  power  required  per  car  is,  for 
an  approximation,  nearly  double  that  required  for  a  stand- 
ard double  truck  car  in  street  railway  work.  The  speed 
of  the  interurban  car  is  nearly  double,  and  the  car  itself  is 
often  heavier.  On  the  other  hand  the  average  live  load  is 
likely  to  be  smaller  and  the  power  wasted  in  stopping  and 
starting  is  less.  On  the  ordinary  urban  railway  twenty 
to  twenty- five  amperes  per  car  is  not  far  from  the  aver- 
age power  required  through  the  day;  on  a  busy  interurban 
line  forty  to  forty-five  are  likely  to  be  required,  or  thirty 
to  forty  if  the  traffic  be  moderate. 

Consequently  heavier  motors  are  often  employed  than 
on  street  railways,  although  for  many  cases  they  are  un- 
necessary. If  the  traffic  is  likely  to  be  large  or  if  the  speed 


TNTERURBAN  AND  CROSS  COUNTRY  WORK.     22/ 

is  to  be  carried  toward  the  higher  limits  mentioned  extra 
large  motors  should  always  be  used. 

Figs.  115  and  116  show  motors  especially  planned  for 
interurban  and  similar  work.  They  are  of  the  usual  Gen- 
eral Electric  and  Westinghouse  types  respectively  and  may 
be  classified  as  of  forty  to  fifty  horsepower.  They  are  fully 
up  to  the  speeds  and  loads  needed  for  heavy  interurban  serv- 
ice and  are  coming  into  extensive  use  for  this  purpose.  In 
general  construction  and  arrangement  they  are  closely  sim- 
ilar to  the  standard  street  car  motors  of  the  same  makes, 
and  are  habitually  worked  with  series  parallel  control, 


FIG.  115. 

which  may  properly  be  considered  a  necessity  for  economi- 
cal operation.  The  saving  by  such  control  in  interurban 
work  is,  of  course,  less  than  usual,  since  the  motors  are  in 
parallel  most  of  the  time,  but  the  device  is  very  necessary 
to  bring  the  speed  within  reasonable  limits  in  running 
through  towns. 

Except  for  the  unusual  size  of  the  motors  and  the  gen- 
eral use  of  power  brakes  there  is  little  peculiar  in  the  car 
equipment  necessary  for  interurban  work.  The  trolley  and 
its  connections  are  quite  as  usual  and  the  method  of  oper- 
ation is  unchanged. 

The  trolley  wire,  too,  is  of  the  same  character  and  sus- 
pended in  the  same  way  as  for  ordinary  street  railway  work. 


228    POWER    DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 

It  is  advisable,  however,  to  use  a  larger  trolley  wire  than 
usual,  not  at  all  to  secure  larger  area  of  contact  with  the 
trolley,  for  this  is  needless,  but  to  simplify  the  feeding 
system.  The  larger  the  trolley  wire,  the 'easier  it  is  to 
equalize  the  voltage  along  the  line.  Nothing  smaller  than 
No.  oo  should  be  used  and  No.  ooo  or  No.  oooo  may  often 
be  useful.  These  larger  sizes  require  special  precautions 
in  suspension,  but  sometimes  are  worth  the  trouble.  In 
most  interurban  work  the  bracket  suspension  can  be  freely 
used  and  is  advisable,  being  cheaper  and  easier  to  keep  up 
than  the  crosswire  suspension. 


FIG     Il6. 

The  supply  of  power  to  an  interurban  line  can  best 
be  illustrated  by  working  out  the  details  of  a  concrete 
case.  We  may  take  for  this  the  hypothetical  line  discussed 
at  the  end  of  the  last  chapter,  selecting  for  discussion  the 
first  case,  using  two  stations  for  the  line. 

Fig.  1 17  is  a  diagram  of  the  system.  Here  A  and  B  are 
the  termini,  C  and  D  intermediate  towns  which  may  have  an 
influence  on  the  distribution  of  the  power  and  E  and  F  the 
points  selected  for  the  power  stations  in  Chap.  VII.  The 
track  is,  as  will  usually  be  the  case  in  such  roads,  a  single 
track  with  turnouts.  The  distance  from  A  to  B  is  thirty 
miles,  from  A  to  C  about  five  miles  and  from  D  to  B  twelve 


INTKRURBAN   AND   CROSS   COUNTRY   WORK.  2  29 

miles.  In  the  previous  discussion  the  load  was  assumed 
uniform  along  the  line.  Obviously  it  is  unlikely  to  be  so, 
and  we  must  accordingly  modify  the  simple  arrangement 
there  shown.  We  may  still  allow  the  fifty  amperes  per 
car  as  before.  The  exact  effect  of  C  and  D  on  the  inter- 
urban  traffic  cannot  possibly  be  foretold,  and  indeed  it  will 
constantly  be  subject  to  some  variation,  nevertheless  cer- 
tain things  can  be  safely  predicted. 

The  local  traffic  between  C  and  A  will  have  the  effect 
of  shifting  the  load  centre  of  the  section,  E  A,  toward  A. 
Similarly  the  traffic  between  D  and  B  will  shift  the  load  on 
the  right  hand  side  of  the  section,  K  F,  somewhat  toward  F. 
If  the  towns,  C  and  D,  are  of  nearly  the  same  size,  the  two 
halves  of  the  line  will  be  about  equally  loaded,  so  that  the 
stations  will  be  of  the  same  size.  E  D  will  assuredly  be 
the  most  lightly  loaded  section  of  the  line. 


H- 
T-! 


Di<  ---  M  ---  >iF 


-12-m.- 


FIG.    117. 

Now  what  conclusion  as  to  the  distribution  of  power 
are  we  justified  in  making?  Although  some  data  are  avail- 
able as  to  purely  urban  traffic  in  cities  of  known  size,  there 
are  as  yet  no  data  for  predicting  the  probable  actual  travel 
on  an  interurban  line.  The  assumption  as  to  current  re- 
quired is  as  close  a  guess  as  one  would  be  justified  in  mak- 
ing. Any  change  in  the  distribution  of  feeder  copper,  due 
to  assumed  differences  of  load  in  different  parts  of  the  line, 
is  somewhat  hazardous,  and  about  the  only  change  author- 
ized by  the  evidence  is  a  change  of  position  of  the  station, 
E.  A  situation  at  or  near  C  is  certainly  an  improvement. 
It  might  be  advantageous  to  make  F  equidistant  from  D 
and  B,  but  in  view  of  the  shift  in  E  it  probably  would  not 
be  desirable  to  further  increase  the  distance  between  sta- 
tions. Throughout  we  assume  that  the  real  local  traffic 
over  our  line  in  A  and  B  is  small,  owing  to  local  street 
railways. 


230  POWER   DISTRIBUTION   FOR  ELECTRIC   RAILROADS. 

We  may  now  lay  out  the  system  as  shown  in  Fig.  118 
and  plan  the  stations  and  feeders.  We  have  two  stations, 
E  and  F,  of  equal  size,  each  supplying  half  the  whole  line, 
A  B.  The  station,  E,  however,  serves  a  line  five  miles  in 
one  direction  (E  A)  and  ten  miles  in  the  other  (E  G)  to 
G,  the  center  of  the  line.  The  station,  F,  feeds  7^  miles 
each  way.  Each  of  these  stations  must  be  able  to  furnish 
a  maximum  current  of  about  600  amperes  and  an  average 
output  ot  about  half  this.  The  voltage  should  be  as  great 
as  the  standard  generators  can  conveniently  give,  say,  600 
volts  as  a  maximum. 

If  we  are,  as  in  the  previous  discussion,  to  allow  fif- 
teen per  cent  loss  at  full  load,  ten  per  cent  in  the  feeders 
and  five  per  cent  in  the  trolley  wire,  the  generators  may 


,;;:;,,;_,_,;      . „  <-._"£]   j  j  |  !  j   j  \  !  j  i  '        ''  \    250000  C.   TO..  |250000  C.   IT 

l«WOOO  c."m.J ""5WOW  cr^  '^pj       ilii!^--—!-—^  ^  ^ 

Street  Ry.JounuJ 

FIG.    Il8. 

well  be  given  an  overcompounding  for  ten  per  cent,  thus 
taking  care  of  the  loss  in  the  feeders. 

Each  station  should  be  equipped  in  duplicate,  partially 
at  least.  The  maximum  continued  output  at  any  time  we 
have  assumed  at  360  k.  w. ,  600  amperes  at  600  volts.  The 
average  output  is  about  180  k.  w.  and,  save  at  special 
times,  the  maximum  output  would  be  considerably  less 
than  that  noted  above.  If  at  each  station  were  installed 
two  generators,  of  225  to  250  k.  w.  output  apiece,  one  of 
these  would  handle  the  whole  load  of  the  station  during  a 
considerable  part  of  the  day,  and  the  second  could  be 
thrown  in  on  the  heavy  hours  or  all  day  on  special  occa- 
sions. In  case  of  accident  to  a  dynamo  or  an  engine  the 
remaining  one  could  keep  up  the  service  without  serious 
interference  with  traffic,  particularly  if  the  feeders  were 
arranged  judiciously. 

As  regards  the  arrangement  of  these  units  it  is  rather 
an  open  question  between  direct  coupling  and  direct  belt- 


INT3RURBAN  AND  CROSS  COUNTRY  WORK.     231 

ing  in  a  plant  of  this  size,  with,  perhaps,  the  weight  of  ad- 
vantage rather  in  favor  of  the  former  alternative.  At  this 
output,  however,  one  is  quite  near  the  point  at  which  the 
construction  of  direct  coupled  machines  becomes  embarrass- 
ing on  account  of  low  speed,  and  it  often  happens  that  the 
belted  plant  is  not  only  cheaper,  but  more  efficient.  It 
most  emphatically  does  not  pay  to  couple  directly  to  a  sim- 
ple, non-condensing  engine,  instead  of  belting  to  a  Corliss 
type  engine  in  a  plant  of  this  size.  It  always  pays  to  con- 
dense, and  it  nearly  always  pays  to  use  compound  engines. 
The  simple,  single  valve,  non-condensing  engine  is  an  eco- 
nomic abomination  in  such  a  plant,  and  should  not  be  con- 
sidered for  a  moment.  The  author's  choice  would  be  a 
compound  condensing  engine,  with  independent  admission 
and  exhaust  valves,  running  not  less  than  120  to  150 
r,  p.  m.  Such  an  engine  plant  will  produce  power  at 
about  two-thirds  the  cost  by  ordinary  simple  engines,  and 
very  nearly  as  cheaply  as  the  best  that  can  be  done  under 
similar  circumstances  by  the  best  triple  expansion  engines- 
which,  in  a  plant  of  the  size  considered,  are  less  suited  to 
the  conditions  of  variable  load  than  compound  engines. 

We  may  now  take  up  the  distribution  step  by  step. 
For  a  constant  we  may  safely  take  14,  as  representing  the- 
case  of  a  good  track  and  moderately  heavy  traffic. 

Beginning  with  the  section  E  A,  we  may  safely  assume 
that  about  one-fourth  the  total  load  will  be  concentrated 
upon  it,  and  uniformly  distributed.  We  will  assume  a 
No.  ooo  trolley  wire  of  167,000  c.  m.,  weighing  2677  Ibs. 
per  mile.  This  wire  will  carry  100  amperes,  the  maximum 
current  for  a  single  car,  over  4000  ft.,  with  moderate  loss 
of  voltage.  Three  cars  normally  belong  on  the  section, 
and  we  must  meet  the  contingency  of  all  three  being  at  A 
and  loaded,  calling  for,  say,  200  amperes.  In  this  con- 
tingency we  should  be  justified  in  assuming  as  much  as 
100  volts  drop  in  the  feeders  alone,  and  that  not  more 
than  one  other  car  will  be  fairly  upon  the  section.  At  five 
miles  distance  the  delivery  of  200  amperes  under  these 
conditions  calls  for  728,000  c.  m.  This  may  be  very  ad- 


232    POWER  DISTRIBUTION"  FOR  ELECTRIC  RAILROADS. 

vantageously  approximated  by  a  600,000  c.  m.  cable  plus 
the  trolley  wire.  If  this  cable  is  tied  into  the  trolley  wire 
at  frequent  intervals,  say,  every  1000  ft.,  for  a  mile  or  two 
near  A,  the  drop  in  the  trolley  wire  as  such  becomes 
trifling,  and  the  drop  saved  here  may  be  transferred  to 
the  feeder  account.  Nearer  K  the  taps  need  not  be  so  fre- 
quent, and  the  trolley  wire  should  be  directly  connected  to 
the  station.  We  may  then  arrange  this  section  as  shown  in 
Fig.  118  by  the  dotted  lines.  Under  this  arrangement  the 
drop  at  normal  full  load,  with  one  car  at  A,  a  second  nearly 
midway  between  K  and  A,  and  another  near  K,  assuming 
for  current  100  amperes  per  car  would  be  pretty  near  the 
required  fifteen  per  cent,  although,  as  we  have  pre- 
viously seen,  the  conditions  of  extreme  load  must  in  the 
last  resort  determine  the  amount  of  feeder  copper. 

A  feeder  of  600,000 c.m.,  uninsulated,  weighs  1800 Ibs. 
per  thousand  feet  (three  times  the  circular  mils  in  thous- 
ands, as  we  have  already  seen),  hence  we  must  write  down 
against  this  section  about  48,000  Ibs.  of  copper. 

Next  comes  the  long  section  E  G.  On  this  three  or 
four  cars  may  normally  be  operated.  About  the  worst 
that  can  be  expected  is  a  couple  of  cars  near  G 
calling  for  perhaps  150  amperes  together  and  a  similar 
pair  fairly  near  K.  As  to  drop  we  may  here  take  rather 
extreme  measures  and  allow,  so  far  as  station  E  is 
concerned,  a  maximum  drop  of  150  volts.  This  calls  for 
770,000  c.  m.  which  we  can  again  make  up  of  a  600,000 
c.  m.  cable  plus  the  trolley,  the  two  being  frequently  tied 
together.  But  even  this  does  not  properly  take  account  of 
the  second  pair  of  cars.  These  at  worst  cannot  be  ex- 
pected to  be  more  than  five, miles  from  E.  Hence  under 
the  same  conditions  of  drop  the  total  area  of  copper  re- 
quired would  be  385,000  c.  m.  In  connection  with  the 
trolley  wire  a  250,000  c.  m.  cable  would  be  rather  more 
than  enough  to  do  the  work.  This  feeder  should  be  tied 
to  the  trolley  perhaps  every  1000  ft.,  and  should  cover  the 
first  half  of  E  G.  This  pair  of  feeders,  as  shown  in  Fig. 
1 1 8,  complete  the  distribution  system  for  the  station  E.  The 


INTERURBAN  AND  CROSS  COUNTRY  WORK.     233 

main  feeder  here   would  weigh  about  96,000  Ibs.  and  the 
short  feeder  about  20,000. 

We  may  now  take  up  the  station  F  and  its  connec- 
tions. F  is  midway  of  its  section  and  the  only  disturbing 
factor  is  a  small  one,  the  town  D.  Its  tendency  would  be 
to  move  the  load  center  of  the  section  G  F  toward  F  since 
a  town  in  such  a  situation  would  probably  be  tributary  to 
B  rather  than  A. 

The  section  G  F  would  normally  contain  three  or  at  most 
four  cars.  The  worst  concentration  of  load  to  be  expected 
would  be  a  pair  at  G  with  another  pair  between  D  and  F. 
Allowing  150  amperes  for  each  pair  and  a  maximum  of 
twenty-five  per  cent  drop  to  G,  we  find  about  6oo,oooc.  m. 
required.  But  G  can  draw  part  of  its  current  from  E. 
Therefore  we  can  take  advantage  of  this  fact  and  not  only 
use  less  copper  from  F  to  G,  but  reduce  that  from  K  to  G. 
Altogether  we  are  unlikely  to  get  more  than  three  cars  in 
the  vicinity  of  G  calling  for,  say,  200  amperes.  This  would 
call  for  only  about  1,000,000  c.  m.  from  both  stations. 
Since  it  is  desirable  to  give  one  station  the  ability  to  ex- 
tend some  help  to  the  other  it  is  desirable  not  to  cut  down 
the  copper  too  much.  One  of  the  most  practical  ways  of 
doing  this  is  that  shown  in  the  figure.  Reducing  the 
main  feeder  from  K  to  G  to  500,000  c.  m.  we  run  a  similar 
feeder  from  F  out  to  and  beyond  G,  making  the  two  feed- 
ers of  the  same  length.  This  leaves  on  the  section  G  F 
two  cars  unprovided  for.  As  there  may  be  an  occasional 
call  for  extra  conductivity  toward  D,  this  section  may  well 
be  provided  for  by  a  250,000  c.  m.  cable  up  to  D. 

The  500,000  c.  m.  feeder  weighs  1500  Ibs.  per  M  feet, 
and  there  is  ten  miles  of  it,  weighing,  say,  30,000  Ibs., 
which  is  also  the  weight  of  the  revised  feeder  from  B  to  G. 
The  250,000  c.  m.  feeder  weighs  750  Ibs.  per  M  feet  and 
its  total  weight  is  about  15,000  Ibs. 

We  may  now  pass  to  the  final  section,  F  B.  The  con- 
ditions at  B  are  similar  to  those  at  A.  Allowing  200  am- 
peres possible  demand  near  B,  about  750,000  c.  m.  will  do 
the  work  there.  There  may  be,  however,  a  car  or  two 


234    POWER   DISTRIBUTION   FOR   ELECTRIC    RAILROADS. 

elsewhere  on  the  section  at  the  same  time,  calling  perhaps 
for  one  hundred  amperes. 

The  joint  load  can  be  best  taken  care  of  by  a  pair  of 
feeders,  one  to  B  of,  say,  500,000  c.  m.,  the  other  out,  say, 
four  miles  from  F,  of  about  250,000  c.  m.  The  function  of 
the  latter  is  to  handle  cars  within  that  distance  of  F  and 
also  to  improve  the  conditions  at  B.  These  are  shown 
with  the  rest  in  Fig.  118.  The  weight  of  the  main  feeder 
here  would  be  60,000  Ibs.,  that  of  the  small  feeder,  say, 
15,000  Ibs. 

We  can  now  take  account  of  stock  and  find  the  total 
cost  of  copper  for  the  feeding  system.  We  may  tabulate 
as  follows; 

Section.  Wt. 

A  K  48,000 

EG  (main)  80,000 

(adjunct)  20,000 
G'  F  ( long  main )  80,000 

adjunct  18,000 

FB  (main)  60,000 

adjunct  15,000 

321,000 

This  would  cost  at  fifteen  cents  per  pound  about  $48,000, 
a  very  different  figure  from  that  previously  found  by  the 
assumption  that  the  maximum  load  may  be  taken  at  the 
middle  point  of  the  proposed  line  to  be  fed. 

The  existence  of  this  excess  and  the  causes  that  pro- 
duce it  must  be  carefully  examined.  In  the  first  place 
20,000  Ibs.  of  copper,  the  section  of  feeder  G'G  belonging 
to  station  F,  is  directly  chargeable  to  safety  precautions, 
and  is  for  the  purpose  of  enabling  the  two  stations  to  be  of 
some  material  assistance  to  each  other  in  case  of  accident 
to  one  of  them. 

The  large  remaining  discrepancy  is  almost  wholly  due 
to  the  fact  that  the  load  on  an  electric  railway  is  a  shifting 
one.  Instead  of  being  able  to  assume  a  uniform  distribu- 
tion of  the  maximum  load,  it  must  be  treated  as  a  concen- 
trated load,  perhaps  even  at  the  most  unfavorable  point  of 
the  line.  In  fact,  it  often  happens  that  the  maximum  load 


INTKRURBAN  AND  CROSS  COUNTRY  WORK.     235 

must  be  handled  at  the  extreme  end  of  the  section,  instead 
of  the  middle  point.  Since  the  copper  required  varies  as 
the  square  of  the  distance,  this  extreme  position  would  re- 
quire four  times  the  copper  called  for  under  the  original 
hypothesis,  but  on  the  other  hand  for  this  abnormal  load 
much  more  than  the  average  drop  is  allowable. 

In  this  as  in  all  other  railway  work  the  real  invest- 
ment in  copper  is  determined  not  by  the  average  loss  of 
energy  that  may  be  desirable,  but  by  the  maximum  drop 
permissible  under  the  worst  conditions  of  load.  This  con- 
dition weighs  heavily  on  interurban  lines,  since  where  a 
network  is  possible,  the  various  parts  of  it  will  not  be 
loaded  simultaneously  and  can  help  each  other  out,  while 
on  a  straightaway  line  each  section  of  conductor  must  act 
for  the  most  part  independently.  In  a  long  interurban 
road  of  this  character  the  booster  may  often  find  a  legiti- 
mate and  important  use.  If  we  could  depend  on  a 
fairly  uniform  schedule  of  traffic  the  practical  arrange- 
ment of  the  feeding  system  would  be  much  simplified.  In 
cases  like  the  one  in  hand  there  are  likely,  in  spite  of  care- 
ful operation,  to  come  times  when  cars  are  massed  at  one 
point  on  the  line  to  an  extent  not  contemplated  in  the 
design  of  the  system. 

Suppose  for  example  that  occasionally  extra  cars 
must  be  run  between  A  and  B.  A  circus  comes  to  the 
latter  place  or  some  special  celebration  takes  place  there 
and  it  becomes  necessary  to  accommodate  a  very  unusual 
number  of  passengers  within  a  limited  time.  It  may  then 
be  very  important  to  deliver  double  the  usual  maximum 
current,  say,  as  much  as  400  amperes,  at  B  while  still 
retaining  a  good  working  voltage.  This  the  existing 
feeders  would  be  quite  inadequate  to  maintain,  since  the 
drop  would  be  in  the  vicinity  of  300  volts. 

To  bring  the  working  pressure  to  about  500  volts, 
which  would  be  highly  desirable  to  meet  this  exigency, 
would  require  the  installation  of  something  like  75  tons  of 
copper,  costing  about  $22,500. 

The  best  alternative  is  to  install  a  boosting  dynamo 


236    POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

at  the  station  F,  to  furnish  about  200  additional  volts  on 
the  long  feeder,  F  B.  The  capacity  of  this  booster  should 
be  about  100  k.  w.  and  its  cost,  complete  with  motive 
power,  and  ready  to  run  would  not  be  more  than  $5,000. 
This  would  enable  the  voltage  to  be  kept  up  at  B  under 
most  trying  conditions,  and  would  moreover  enable  station 
F  to  be  of  great  assistance  to  station  E  in  case  of  accident 
to  the  latter.  A  similar  booster  at  E  would  be  able  to 
render  similar  service  at  F  and  to  take  care  of  the  most 
abnormal  loads  at  A.  Ordinarily  these  boosters  would  be 
in  sendee  only  at  infrequent  intervals,  a  few  hours  per  day 
for  a  day  or  two  at  a  time,  but  they  would  be  well  worth 
installing  merely  as  a  precaution,  insurance  as  it  were. 

If  the  loads  on  the  line  become  such  as  to  require  fre- 
quent aid  from  the  boosters  the  economics  of  the  case 
would  have  to  be  looked  into  as  indicated  in  Chap.  IV, 
and  it  might  prove  to  be  wise  to  install  additional  copper. 
In  all  roads  of  this  class  the  local  conditions  must  ulti- 
mately determine  the  character  of  the  feeding  system  for 
the  most  economical  results. 

In  spite  of  this  the  copper  required  in  the  case  in  hand 
is  not  very  formidable.  Unless  the  road  is  operated  on  a 
regular  schedule,  still  more  copper  would  be  required, 
since  if  the  operation  of  the  cars  is  careless  and  irregular, 
more  may  be  massed  at  a  single  point  than  were  allowed 
for  in  the  estimate.  For  economy  in  copper  the  road  must 
be  intelligently  operated  as  well  as  skillfully  planned.  The 
same  uniform  schedule  that  secures  good  and  regular  serv- 
ice throughout  the  line  will  facilitate  good  and  economical 
distribution  of  power.  The  only  reasons  for  unusual 
massing  of  cars  at  one  point  are  accidents  to  the  track  or 
motors  or  very  unusual  demands  for  car  service.  In  the 
former  case,  the  service  can  be  resumed  on  regular  time 
without  any  extraordinary  demand  for  power,  and  in  the 
latter  there  will  be  no  trouble  if  any  extra  cars  that  may 
be  necessary  are  run  in  an  orderly  manner,  as  they  would 
be  on  any  well  conducted  railroad.  Managers  should  bear 
in  mind  that  the  operators  on  an  important  interurban  line 


INTERURBAN  AND  CROSS  COUNTRY  WORK.     237 

should  be  picked  men  of  more  than  usual  skill  and  intelli- 
gence, and  that  it  pays  to  get  such  men.  They  are  worth 
the  extra  cost  merely  as  a  form  of  insurance. 

No  general  rule  can  be  assigned  for  the  increase  in 
feeder  copper  due  to  the  demands  of  heavy  displaced  loads. 
The  amount  and  character  of  the  displacement  varies  in 
different  cases  in  a  way  that  cannot  be  formulated.  The 
only  thing  to  be  done  is  to  take  up  each  case  as  a  special 
problem  as  we  have  just  done. 

The  effect  of  this  extra  copper  on  the  relative  economy 
of  the  various  methods  ot  supply  is  easy  to  approximate. 
Recurring  to  the  estimates  at  the  end  of  the  last  chapter,  it 
is  evident  that  they  need  revision.  The  annual  cost  by 
method  I  will  be  increased  by  the  interest  and  depreciation 
on  the  additional  copper.  Method  II  will  suffer  in  almost 
the  same  ratio  as  method  I,  and  hence  the  absolute  increase 
in  copper  and  the  added  annual  expense  will  be  greater, 
putting  the  booster  method  to  very  serious  disadvantage, 
if  used  without  undue  loss  of  energy  except  as  it  may  be 
adopted  for  emergencies,  as  just  described. . 

Method  III,  which  really  consists  in  transmitting 
power  at  high  voltage  from  K  to  F  (Fig.  118),  is  affected  to 
precisely  the  same  absolute  extent  as  method  I,  and  there- 
fore has  practically  the  same  relative  value  as  before. 

Method  IV  must  take  into  account  the  same  condi- 
tions of  displaced  load  that  influence  the  other  cases,  but 
in  a  somewhat  different  way.  The  trolley  wire  alone  is 
unable  to  carry  the  current  for  a  severe  load  any  consider- 
able distance,  hence  it  must  be  reinforced  unless  the  line 
is  to  be  supplied  with  an  exaggerated  transformer  capacity 
and  the  transformers  are  placed  very  near  together.  To 
give  a  good  practical  distribution  of  power  there  must  be 
sufficient  feeder  capacity  to  easily  carry  the  current  for  the 
extreme  loads  already  mentioned  without  demanding  trans- 
formers at  too  frequent  intervals.  The  net  result  of  the 
conditions  of  load  will  be,  first,  to  demand  the  installation 
of  feeder  copper  to  distribute  the  energy  delivered  from  the 
transformers,  and  second,  extra  transformer  capacity 


238     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

enough  to  respond  to  the  utmost  calls  of  a  displaced  maxi- 
mum load  In  the  case  before  us  it  would  not  be  wise  to 
subdivide  the  transformer  capacity  greatly,  since  the  in- 
dividual units  would  be  small  and  expensive.  The  maxi- 
mum load  of  1 200  amperes  at  500  volts  will  be  increased 
somewhat  by  lagging  current,  and  no  part  of  the  line  can 
be  left  without  transformer  capacity  enough  to  take  care 
of  the  heaviest  load  to  be  met.  Consequently  the  total 
capacity  of  the  transformers  will  certainly  be  much  greater 
than  the  nominal  600  k.  w.,  probably  at  least  one-half 
greater.  Without  going  far  into  details,  feeders  of  not 
less  than  250,000  c.  m.  would  be  needed  to  reinforce  the 
trolley  wire  for  its  entire  length.  These  would  cost  about 
$18,000  and  in  addition  the  extra  cost  of  transformers  due 
to  their  moderate  size  and  extra  capacity  could  hardly  ag- 
gregate less  than  $5000  more.  Hence  an  annual  charge 
of  about  $2300  must  be  added  to  the  annual  cost  of  powei 
obtained  in  the  last  chapter.  This  leaves  the  distribution 
by  alternating  current  in  the  same  relative  position  of  ad- 
vantage as  before,  a  position  which  is  the  stronger  as  the 
distances  to  be  covered  grow  greater.  Only  when  the  serv- 
ice undertaken  is  exceedingly  heavy  can  distributed  sta- 
tions compete  with  a  good  alternating  transmission,  and 
the  latter  always  has  the  possible  use  of  water  power  or 
utilization  of  cheap  coal  to  its  credit. 

A  very  striking  instance  of  the  value  of  transmission 
to  alternating  motors  is  given  by  the  Burgdorf  road  de- 
scribed in  the  last  chapter.  Here  full  advantage  is  taken 
not  only  of  the  economies  of  transmission  but  of  the  facil- 
ity with  which  polyphase  motors  may  be  worked  at  volt- 
ages considerably  higher  than  500  volts.  The  result  is 
that  in  spite  of  a  heavier  load  than  is  here  assumed,  no 
low  tension  feeders  are  employed  and  the  total  cost  of  cop- 
per is  hardly  more  than  we  have  here  taken  for  the  cost 
of  auxiliary  feeders  alone. 

Allowance  must  be  made,  however,  for  the  fact  that 
in  Switzerland  copper  is  more  expensive  and  transformers 
are  materially  cheaper  than  in  this  country.  Here  the 


INTERURBAN  AND  CROSS  COUNTRY  WORK.     239 

legitimate  tendency  would  be  to  use  fewer  transformer 
stations  and  more  copper  than  in  the  foreign  case. 

With  750  volt  motors  the  weight  of  copper  required 
for  the  distribution  would  come  down  to  about  one-half 
of  that  which  we  have  assumed  and  the  whole  amount 
could  be  conveniently  placed  in  the  working  conductors. 
As  to  number  and  location  of  transformer  stations,  the 
most  beautiful  feature  of  the  whole  method  is  that  these 
can  be  placed,  without  any  material  variation  of  cost,  just 
where  they  will  do  the  most  good.  On  the  road  that  we 
have  assumed  for  investigation  the  most  advantageous 
number  would  probably  be  somewhere  between  six  and 
ten.  The  natural  locations  would  be  near  A,  B,  C  and  D 
respectively,  between  C  and  D,  and  between  D  and  B. 
The  distribution  in  number  and  position  would  be  gov- 
erned by  the  distribution  of  the  load.  It  may  often  be 
convenient  too,  to  vary  the  size  of  the  individual  trans- 
former stations  so  as  to  best  meet  local  conditions,  and 
the  system  as  a  whole  is  wonderfully  economical  and 
flexible. 

Very  different  in  character,  but  nevertheless  allied  in 
function  to  interurban  roads  are  those  which  we  have  de- 
signated as  cross  country  roads. 

It  is  surprising  to  realize  how  small  a  part  of  this  or 
any  other  country  is  conveniently  tributary  to  existing 
railway  lines  of  any  kind.  A  glance  at  the  map  of  any 
well  settled  state  will  show  many  townships  not  touched 
by  any  railway  and  many  more  only  reached  in  round- 
about ways.  It  is  not  uncommon  to  find  a  rich  farming 
district  almost  without  means  of  communication  with 
neighboring  cities  and  totally  devoid  of  facilities  for  inter- 
communication betweens  its  parts  save  in  the  good  old 
fashioned  way.  Nearly  one-seventh  of  the  towns  in  Mas- 
sachusetts are  without  railway  stations.  Within  fifteen 
miles  of  Boston  is  one  whole  township  untouched  by  a 
railway  of  any  kind,  steam  or  electric.  In  the  less  popu- 
lated states,  there  are  many  fine  regions  that  are  quite 
isolated. 


240    POWER  DISTRIBUTION  FOR  ELECTRIC   RAILROADS. 

Railroads  have  left  these  regions  untouched  because 
a  route  elsewhere  would  pay  better,  or  would  give  pros- 
pects of  traffic  sufficient  to  float  a  heavier  capitalization 
without  creating  undue  suspicion. 

There  are,  of  course,  plenty  of  cases  in  which  an  ordi- 
nary railroad,  even  a  branch,  would  not  pay  and  conse- 
quently is  not  built,  while  the  prospects  of  traffic  are  yet 
quite  near  the  paying  point.  A  railroad  is  a  rather  in- 
flexible thing  at  best.  It  requires  a  nearly  level  track, 
must  avoid  severe  curves,  has  often  to  acquire  an  expen- 
sive right  of  way  and  is  in  general  subject  to  restrictions 
and  limitations  in  such  wise  as  to  render  construction  and 
operation  somewhat  too  costly  for  many  places  that  are 
yet  in  the  aggregate  of  considerable  importance.  Espec- 
ially in  the  agricultural  regions  there  is  much  rather  scat- 
tered freight  traffic  which  cannot  be  easily  handled  by  an 
ordinary  road  at  paying  rates,  but  could  be  profitably 
gathered  and  increased  by  roads  built  with  this  specific 
object  in  view. 

Abroad  much  has  been  done  in  the  way  of  building 
light  railways  especially  for  the  purpose  of  developing 
agricultural  districts.  Most  of  them  are  narrow  gauge,  be- 
tween two  and  three  feet,  although  a  few  conform  to  the 
existing  standard  gauges  for  convenience  in  exchanging 
and  transmitting  cars.  In  Belgium  and  Prussia  especially 
this  class  of  service  is  very  considerable  in  amount,  although 
there  are  roads  of  this  kind  all  over  the  Continent  and  not 
a  few  in  England  and  English  colonies.  Owing  to  foreign 
habits  of  railway  construction  most  such  lines  are  from 
our  standpoint  too  expensive,  costing  in  general  from  a 
minimum'  of  $7500  to  $  15,000  or  more  per  mile  to  build 
and  equip. 

In  this  country  there  was  fifteen  or  twenty  years  ago 
an  epidemic  of  narrow  gauge  construction,  generally  re- 
sulting in  a  change  to  standard  gauge; 

The  truth  is  that  while  these  light,  narrow  gauge  rail- 
roads can  be  built  and  equipped  quite  cheaply,  often  for 
half  the  cost  of  standard  construction,  they  are  seldom 


INTERURBAN   AND   CROSS   COUNTRY   WORK.  241 

cheap  enough  to  give  much  advantage  when  they  attempt 
serious  railway  service.  In  competition  with  regular  lines, 
they  soon  find  themselves  handicapped,  and  for  purely 
local  purposes  they  generally  are  too  costly. 

The  need  in  very  many  cases  is  for  feeding  lines  to 
facilitate  the  movement  of  commodities  and  passengers 
now  laboriously  hauled  over  country  roads.  For  this 
specific  purpose  the  first  consideration  is  cheapness;  these 
lines  would  not  come  into  competition  with  existing  rail- 
roads, hence  there  is  no  need  for  more  than  very  moderate 
speeds;  there  is  no  need  of  handling  heavy  trains;  light 
passenger  cars  and  freight  skips  are  quite  sufficient.  The 
moment  one  attempts  to  use  standard  gauge  and  exchange 
cars  with  through  lines  heavy  construction  is  necessary  to 
stand  the  wear  and  tear,  and  the  cost  becomes  too  great  for 
the  purpose  in  hand. 

For  this  cross  country  service  electric  construction  is 
singularly  well  suited.  Grading,  always  an  item  of  ex- 
pense to  be  feared,  is  much  reduced  with  an  electric  road, 
for  while  two  or  three  per  cent  grades  are  all  that  would 
be  attempted  in  ordinary  light  railway  construction,  ten 
per  cent  is  perfectly  practicable  for  an  electric  car  with  a 
light  trailer  or  two. 

A  gain  equally  important  is  the  weight  of  the  motive 
power.  Instead  of  a  locomotive  weighing  six  to  ten  tons, 
the  dead  weight  of  the  motor  need  not  much  exceed  half  a 
ton,  which,  with  all  the  load  in  the  motor  car,  is  available 
for  securing  adhesion.  With  this  lessened  weight  to  be 
carried  the  track  construction  can  be  lightened  and  cheap- 
ened correspondingly. 

In  spite  of  the  singular  fitness  of  electric  service  for 
this  particular  and  most  useful  purpose,  little  has  as  yet 
been  done.  Perhaps  the  reason  is  lack  of  popular  apprecia- 
tion of  the  exact  conditions  to  be  met.  The  danger  lies  in 
trying  to  do  too  much,  in  building  an  ordinary  cheap  elec- 
tric railroad,  instead  of  something  little  more  elaborate 
than  a  telpher  line;  in  trying  for  a  speed  of  twenty  miles 
per  hour  where  ten  is  amply  sufficient. 


242   POWER  DISTRIBUTION  FOR  ELECTRIC  RAILROADS. 

To  meet  the  need  of  small  places  for  transportation 
facilities  one  must  cut  his  coat  according  to  his  cloth.  A 
little  hard  common  sense  applied  to  the  problem  will  result 
in  the  establishment  of  many  a  most  useful  line,  giving 
greatly  increased  facilities  for  intercommunication,  and 
yielding  good  returns  on  a  small  investment. 

A  standard  gauge  (4  ft.  8^  ins. )  electric  railway  track 
can,  if  the  grading  is  trivial  and  the  route  is  generally  easy, 
be  put  in  position  for  a  total  cost  of  as  little  as  $5000  per 
mile  of  single  track,  exclusive  of  bridges  and  other  special 
construction  and  right  of  way,  using  ordinary  cars  and  car 
equipments.  This  supposes  T  rail  of  forty  to  forty-five 
pounds  per  yard  and  economy  everywhere.  The  cost  of 
overhead  wire,  bonding,  equipment  and  station  per  mile, 
of  course,  depends  entirely  on  the  service.  For  a  road, 
say,  ten  miles  in  length,  very  economically  equipped,  $4000 
to  $5000  per  mile  may  be  enough.  In  other  words,  the 
cheapest  feasible  price  for  building  and  equipping  a  stand- 
ard gauge  electric  road  is  somewhere  about  $9000  to 
$10,000  per  mile,  anything  under  $10,000  being  extraordi- 
narily low. 

Now  for  the  work  properly  belonging  to  cross  country 
roads  that  figure  is  often  prohibitively  high.  In  order  to 
do  the  work  at  a  less  price,  radical  changes  have  to  be 
made  in  the  structure.  For  localities  where  grading  is 
slight,  and  there  is  not  likely  to  be  much  trouble  from  snow, 
light,  narrow  gauge  roads  meet  the  conditions  fairly  well. 

Foreign  practice  gives  valuable  data  in  this  line. 
For  a  gauge  of  o.  6  metre  frequently  used  abroad  (practically 
two  feet),  a  rail  weighing  about  twelve  kilos  per  metre 
(twenty-five  pounds  per  yard)  is  freely  used.  The  sub- 
structure can  be  light  in  proportion,  for  the  rolling  stock 
is  also  light,  albeit  the  locomotives  are  decidedly  heavier 
than  a  loaded  motor  car  would  usually  be.  We  must  re- 
member that  with  light  cars,  comparatively  low  speeds  and 
rather  infrequent  service,  a  light  rail  can  be  safely  used, 
and  will  give  no  more  trouble  than  heavy  track  under  ordi- 
nary street  railway  service. 


INTERURBAN  AND  CROSS  COUNTRY  WORK.     243 

A  twenty-four  inch  gauge  track,  laid  with  thirty 
pound  rails,  can  be  put  down  under  favorable  circum- 
stances for  about  $3500  per  mile.  Then  comes  the  bond- 
ing and  the  erection  of  the  overhead  structure.  The 
amount  of  wire  required  for  such  a  line  is  comparatively 
small,  for  the  power  also  is  small. 

For  a  line  ten  miles  in  length,  two  trains  in  steady 
service,  each  consisting  of  a  light  motor  car  and  a  freight 
skip,  would  meet  all  ordinary  requirements.  The  total 
weight,  loaded,  should  not  often  exceed  ten  tons.  To  drag 
this  load  on  a  level  track  at  eight  miles  per  hour  requires 
about  seven  horse  power  at  the  car  wheels.  As  grades 
would  naturally  be  taken  at  a  somewhat  lower  speed,  the 
power  required  would  not  increase  very  greatly,  and  an 
expenditure  of  fifteen  horse  power  at  the  wheels  would 
seldom  have  to  be  exceeded. 


FIG.  119. 

In  reckoning  the  copper  we  should  have  to  allow  for 
the  delivery  of  about  thirty  amperes  to  the  train.  With 
600  volts  initial  pressure,  and  allowing  one  hundred  volts 
drop  at  the  end  of  the  line,  it  appears  that  the  copper  re- 
quired is  trifling.  Using  1 3  as  the  constant  in  our  stock 
formula,  the  wire,  supposing  the  station  to  be  at  the  cen- 
ter of  the  line,  conies  out  No.  o,  which  may  conveniently 
be  suspended  as  the  trolley  wire. 

For  economy  bracket  construction  should  be  used, 
unless  circumstances  require  cross  suspension,  in  which 
case  the  very  neat  diagonal  suspension,  due  to  J.  C.  Henry, 
is  the  cheapest  and  most  convenient  method  for  light 
work.  This  is  shown  in  Fig.  119.  Here  A,  B,  C,  D,  K,  etc. , 
are  the  poles  set  in  the  usual  way,  100  to  125  ft.  apart,  but 
alternately  on  either  side  of  the  track.  The  suspension 
wire  is  strung  from  pole  to  pole,  as  shown,  and  the  trolley 


244   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

wire  hung  from  it  in  the  ordinary  manner.  It  is  a  very 
neat  and  cheap  arrangement  where  only  a  trolley  wire  of 
moderate  size  has  to  be  carried.  For  either  this  or  bracket 
construction  fifty  poles  per  mile  are  sufficient,  costing,  laid 
down,  say,  $125.  Setting  in  country  districts  ought  not 
to  cost  more  than  $1.50  per  pole,  bringing  the  pole  line  in 
place  to  about  $200  per  mile.  The  trolley  wire  would  cost 
about  $275  per  mile,  and  suspension  wire,  insulators, 
brackets  and  so  forth,  about  $200  additional,  making 
about  $675  per  mile  for  overhead  structure  and  material. 
For  bonding  the  track  and  suspending  the  trolley  wire,  to- 
gether with  incidental  expenses,  $300  to  $400  per  mile  is 
sufficient. 

Bringing  these  items  together  we  may  say  roundly 
that  with  rigid  economy  $900  to  $1000  per  mile  will  pro- 
vide the  electrical  structure  and  connections  for  such  a 
road  as  that  under  consideration.  Taking  the  larger  figure 
we  see  that  the  electric  narrow  gauge  track  can  be  built 
complete  ready  for  traffic  for  about  $4500  per  mile. 

For  a  ten  mile  road,  the  car  equipment  should  be,  say, 
two  motor  cars  with  an  extra  motor  in  reserve  and  four 
freight  skips  and  a  couple  of  freight  cars  of  a  larger  size. 
The  whole  outfit  should  not  cost  over  $5500  delivered  and 
ready  for  action. 

Now  for  the  station  and  other  equipment.  A  genera- 
tor of,  say,  forty  kilowatts,  and  a  fifty  horse  power  engine 
and  boiler  equipment  is  sufficient.  Boiler  and  engine 
should  be  of  the  simplest  kind  and  the  whole  plant  as  com- 
pactly arranged  as  possible,  since  it  should  ordinarily  be 
operated  by  a  single  capable  man.  Engine,  boiler  and 
generator  set  up  ready  for  operation  should  not  cost  in  the 
aggregate  more  than  $4000.  This  is  enough  to  provide  a 
thoroughly  well  built,  durable  equipment  on  which  the  re- 
pairs should  be  very  light. 

-A  combined  power  station  and  car  house,  with  iron 
stack  for  the  boiler,  should  cost  complete  not  over  $2000, 
and  $500  more  would  provide  waiting  rooms  and  freight 
platforms  at  the  ends  of  the  line. 


INTERURBAN  AND  CROSS  COUNTRY  WORK.     245 

Altogether  these  items  of  construction  and  equipment 
would  aggregate  $12,000,  or  $1200  per  mile. 

Bringing  together  the  various  items  reduced  to  the 
basis  of  cost  per  mile,  we  have  for  a  ten  mile  road" 

Roadbed  and  track  $35oo 

Electrical  construction  1000 

Rolling  stock  550 

Power  station  and  buildings    650 


Total  l57oo 

An  addition  of  $300,  bringing  up  the  total  cost  to 
$5ooo  per  mile,  would  provide  for  all  normal  contingencies 
of  construction.  It  is  safe  to  say  that  in  most  situations  a 
good  narrow  gauge  electric  line  can  be  built  and  equipped 
for  this  sum  if  right  of  way  can,  as  would  nearly  always 
be  the  case,  be  obtained  along  the  public  road. 

This  is  a  reduction  of  about  $4000  per  mile  over  sim- 
ilarly close  figures  for  a  cheap  ordinary  electric  road,  a  dif- 
ference that  would  turn  the  scale  from  loss  to  profit  in 
many  country  localities. 

The  cost  of  operating  such  a  road  is  correspondingly 
low.  The  hours  of  running  need  not  be  eighteen  or 
twenty  as  in  street  railways,  but  could  be  so  reduced  that 
the  work  could  be  arranged  for  a  single  set  of  men  with- 
out unreasonably  long  hours.  A  total  force  of  six  men 
could  operate  the  line  without  difficulty.  Of  these  two, 
the  engineer  and  superintendent  who  should  understand 
the  motors  and  linework  well,  would  probably  have  to  be 
paid  $75  per  month  each;  the  other  four  could  be  obtained 
in  most  country  districts  for  about  $45  per  month  each. 

Under  ordinary  circumstances  the  mechanical  output 
at  the  station  would  not  exceed,  say,  250  h.  p.  hours  per 
day.  Counting  five  pounds  of  coal  per  horse  power  hour 
the  daily  fuel  consumption  would  be  a  little  over  half  a 
ton  of  coal  per  day  costing,  at  $3  per  ton,  in  round  numbers 
$600  per  year.  $400  per  year  more  should  cover  ordinary 
repairs  and  incidental  expenses  at  the  power  station.  An- 
other addition  of  $500  should  cover  taxes  and  miscellaneous 


246    POWER  DISTRIBUTION  FOR  ELECTRIC  RAILROADS. 

expenditures,  making  in  all  very  nearly  $5500  per  year  as 
the  total  expense  account,  irrespective  of  depreciation  and 
interest. 

Roads  such  as  we  are  considering  have  the  advantage 
of  being  able  to  charge  relatively  more  than  urban  lines, 
and  with  a  tolerable  passenger  service,  express  and  mail 
service  and  freight  traffic  should  be  able  to  pick  up  a  very 
satisfactory  living.  The  ten  mile  line  in  question  must 
show  gross  earnings  of  about  $9000  per  year  to  pay  a  fair 
return  on  the  investment  and  set  aside  a  tolerable  sinking 
fund — practically  $24  per  day,  or  $12  per  train  per  day. 
As  each  of  the  two  trains  should  make  six  or  eight  single 
trips  per  day  it  appears  that  the  road  would  pay  on  gross 
receipts  of  $2  per  trip,  twenty  cents  per  train  mile. 


FIG.    120. 

It  is  a  lean  region  indeed  that  cannot  furnish  that 
amount  of  patronage. 

But  this  is  by  no  means  the  last  word  on  cheap  cross 
country  lines.  It  is  quite  certain  that  there  are  available 
constructions  cheaper  than  the  narrow  gauge  just  described. 
At  least  two  existing  arrangements  are  capable  of  a  lower 
minimum  cost  of  construction  than  that  mentioned.  Cur- 
iously enough  both  of  them  have  been  zealously  exploited 
for  heavy  high  speed  railway  work  for  which  they  are  not 
in  the  least  needed,  instead  of  being  pushed  into  a  most 
useful  field  to  which  they  are  well  adapted  and  in  which 
they  have  decided  advantages. 

One  of  these  is  the  well  known  ' '  Boynton  Bicycle' '  road 
of  which  an  excellent  idea  is  given  by  Figs.  120  and  121, 


INTERURBAN   AND   CROSS   COUNTRY   WORK. 


247 


Fig.  1 20  shows  the  appearance  of  the  construction  across 
the  country.  Fig.  121  shows  an  end  view  of  the  narrow, 
pointed  car  in  position  on  the  single  railed  track.  The 
upper  bearing  carried  by  the  brackets  extended  from  the 


FIG.    121. 

heavy  side  poles  along  the  line  is  merely  a  steadying  rail 
whose  function  it  is  to  hold  the  car  upright  when  at 
rest  and  guide  it  around  curves  when  in  motion.  In 
normal  running  the  pressure  against  this  upper  guide  is 
trifling.  All  the  weight  is  carried  by  the  central  double 
flanged  wheels  on  the  track  rail.  The  cuts  are  from  pho- 


248   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

tographs  of  the  experimental  track  on  I,ong  Island.  The 
apparatus  here  was  on  a  considerable  scale,  as  high  speed 
was  attempted  without  conspicuous  success,  probably 
owing  to  a  track  too  short  for  speed. 

Nevertheless,  a  glance  at  the  cuts  shows  how  readily 
and  neatly  the  system  can  be  applied  to  cross  country  roads 
with  light  cars  operated  at  very  moderate  speeds.  Under 
these  circumstances  the  upper  supporting  structure  having 


.  122. 


little  strain  upon  it  can  be  light  and  cheap,  while  a  mere 
row  of  short  posts  rising  just  far  enough  from  the  ground 
to  assist  in  the  grading  may  serve  to  carry  a  light  but  rather 
deep  girder  rail  ,  quite  strong  enough  for  the  traffic.  The  rails 
would  serve  admirably  as  conductors  since  even  a  fifteen 
pound  rail  is  far  more  than  the  equivalent  of  the  copper 
required  and  the  lower  rail  being  off  the  ground  would  be 
little  troubled  by  snow  in  winter.  The  supply  of  power  is 
thus  very  easy  and  simple  and  the  cost  of  grading  is  in 
great  measure  averted. 

Another  construction  which  can  be  carried  out  very 
cheaply  on  the  scale  necessary  for  cross  country  roads  is 
the  saddleback  railway.  The  Meigs  elevated  structure  is 


INTERURBAN  AND  CROSS  COUNTRY  WORK. 


249 


s  good  specimen  of  this  type,  which  has  been  successfully 
worked  up  as  an  electric  line  in  the  Beecher  railway,  an 
experimental  section  of  which  has  been  put  in  use  near 
Waterport,  N.  Y. 

This  arrangement  is  shown  in  Figs.  122  and  123  cf 


FIG.  123. 

which  the  first  shows  a  car  on  the  experimental  track,  and 
the  second  gives  the  essential  details  of  the  structure. 

It  is,  as  shown  in  Fig.  123,  a  quasi-elevated  road  com- 
posed of  posts  or  similar  supports  carrying  longitudinal 
stringers  which  support  the  central  bearing  rail  and  the 
lateral  guide  rails.  These  latter  serve  to  steady  the 
car,  but  are  under  very  little  stress  when  the  car  is  in 
motion. 


250     POWER   DISTRIBUTION  OF  ELECTRIC   RAILROADS. 

As  in  the  bicycle  railway,  very  little  grading  is  nec- 
essary— none  under  favorable  conditions — the  rails  serve 
admirably  as  conductors,  and  the  supporting  structure  is 
cheap  and  simple.  In  the  experimental  road  storage  bat- 
teries were  used,  thereby  throwing  away  one  of  the  essen- 
tial advantages  in  the  conductivity  of  the  rails  and  adding 
unnecessary  weight  to  the  car.  For  cross  country  work- 
ing such  a  system  should  be  a  decided  success  since  it 
could  be  carried  high  enough  to  be  out  of  the  way  at  cross- 
ings and  takes  up  singularly  little  room. 

Either  the  bicycle  or  the  saddleback  road  can  be  in- 
stalled even  more  cheaply  than  the  narrow  gauge  line  just 
discussed,  owing  to  the  practical  abolition  of  grading,  free- 
dom from  an  overhead  trolley  construction  and  full  utiliza- 
tion of  the  rails  as  conductors.  These  roads  too  are  much 
less  liable  to  trouble  from  snow  and  bad  weather  than  the 
narrow  gauge  and  are  equally  efficient  for  the  purpose  in 
hand.  Under  favorable  conditions  they  could  be  built  and 
equipped  for  the  same  service  as  the  narrow  gauge  for  a 
sum  scarcely,  if  at  all,  exceeding  $5000  per  mile  for  a  ten 
mile  line.  At  a  pinch  any  one  of  these  roads  could  get 
along  with  one  man  per  train  exclusive  of  the  men  at  the 
power  house,  thereby  giving  an  electric  railway,  of  which 
the  necessary  expenses  would  be  hardly  more  than  $4000 
per  year,  and  which  would  pay  fairly  on  gross  receipts  as 
small  as  $7500  to  $8000  per  year.  The  possibilities  of  such 
roads  for  opening  up  the  country  are  self  evident. 

Throughout  the  estimates  just  given  it  will  be  noticed 
that  nothing  is  included  for  franchise  and  right  of  way. 
This  omission  is  for  the  very  good  reason  that  in  the 
regions  to  be  benefited  by  such  roads,  franchise  and  way 
would  always  gladly  be  given,  with  not  infrequently  a  sub- 
stantial bonus  in  some  form  or  other. 

Built  for  cash  and  operated  for  profit,  such  roads  offer 
good  prospects  for  excellent  returns  on  the  investment,  and 
their  economic  value  to  the  country  can  hardly  be  over- 
estimated. Almost  nothing  has  yet  been  done  in  this  line, 
but  the  field  is  a  most  promising  one. 


CHAPTER  IX. 

FAST  AND   HEAVY   RAILWAY  SERVICE. 

Up  to  the  present  time  a  large  proportion  of  all  elec- 
tric railway  work  has  belonged  strictly  to  street  railway 
service,  a  few  per  cent  can  be  classed  as  inter  urban,  and 
only  here  and  there  have  there  been  any  serious  attempts 
to  beat  the  locomotive  on  its  own  ground.  The  task  is  a 
serious  one  not  to  be  undertaken  without  good  cause.  Our 
present  locomotive  is  a  wonderfully  reliable  and  efficient 
machine,  beautifully  adapted  for  its  work,  and  if  it  is  to 
be  replaced  by  the  electric  motor,  there  must  be  good  cause 
for  the  change. 

The  economic  relation  between  the  motor  and  the  lo- 
comotive has  been  several  times  carefully  investigated  with 
the  uniform  result  of  showing,  assuming  the  same  condi- 
tions, no  very  considerable  advantage  on  either  side.  It 
is  in  the  variations  in  the  conditions,  the  exigencies  of 
traffic  of  different  kinds,  that  positive  economies  in  favor 
of  electricity  or  of  steam  must  be  sought. 

Without  taking  up  the  application  of  electric  power  to 
universal  railway  work,  there  are  three  classes  of  service 
for  which  it  is  now  admittedly  highly  desirable,  irrespect- 
ive of  any  saving  reckoned  on  the  horse-power-hour  basis, 
which  does  not  completely  tell  the  story  of  ultimate  profits. 
•  In  general  these  three  classes  have  this  in  common, 
that  in  each  of  them  electric  power  gives  positive  advan- 
tage in  earning  capacity,  aside  from  the  saving  in  operat- 
ing cost  which  certainly  exists  in  two  of  them.  The 
classes  in  question  are  as  follows: 

1 .  Heavy  local  passenger  traffic. 

2.  High  speed  interurban  traffic. 

3.  Elevated  roads,  tunnels,  and  special  service. 


252      POWER    DISTRIBUTION    FOR    ELECTRIC   RAILROADS. 

In  the  first  case  experience  has  aucady  taught  the  mag- 
nitude of  the  inroads  made  on  local  passenger  service  by  elec- 
tric railroads  covering  the  same  district.  A  striking  ex- 
ample of  this  has  recently  come  to  the  author's  notice,  in 
which  a  short  steam  road  was  actually  deprived  of  more 
than  ninety  per  cent  of  its  traffic  by  the  operation  of  a 
parallel  electric  system.  Near  every  large  city  the  effect 
of  this  competition  is  severely  manifest  and  is  doubly  seri- 
ous by  reason  of  the  increasing  network  of  electrics  that 
serves  its  territory  so  effectively  as  to  overbalance  the  ex- 
tra speed  of  the  railway  trains. 

That  which  decides  the  route  of  the  suburban  passen- 
ger, in  the  absence  of  any  great  inequality  in  fare,  is  ulti- 
mately the  time  taken  to  travel  from  his  home  to  his  place 
of  business.  Convenient  termini  offset  superior  running 
speed,  and  the  electric  cars  consequently  catch  the  greater 
part  of  the  traffic.  Then  too,  in  the  time  of  the  journey 
must  be  included  probable  delays. 

The  net  result  is  that  where  electric  cars  and  steam 
railways  come  into  competition  for  suburban  or  similar 
business,  the  former  gets  the  lion's  share.  To  give  good 
local  service,  the  cars  or  trains  must  be  frequent,  the  run- 
ning time  fast  and  the  passengers  must  be  delivered  some- 
where near  where  they  wish  to  go.  In  most  cases  steam 
roads  cannot  meet  the  latter  requirement,  consequently 
they  must  compensate  for  its  lack  by  fast  and  frequent 
service.  This  means  short  trains  run  on  short  headway, 
and  right  here  the  locomotive  is  at  a  serious  disadvantage. 
In  the  first  place  the  experience  of  railroads  has  shown 
that  with  increasing  numbers  of  trains  the  cost  per 
passenger  mile  increases.  For  a  given  amount  of  traffic 
carried  in  a  certain  territory,  doubling  the  number  of 
trains  increases  the  cost  per  ton  mile  something  like  fifty 
per  cent. 

That  such  must  be  the  case  is  easily  to  be  seen,  since 
the  number  of  passengers  per  train  is  halved  while  the 
labor  per  train  remains  substantially  the  same,  the  power 
per  train  is  not  very  greatly  decreased,  and  the  investment 


FAST   AND   HEAVY   RAILWAY    SKRVICK,  253- 

and  depreciation  are  increased  by  using  more  locomotives 
for  the  same  service.  In  point  of  fact  for  passenger  serv- 
ice alone  the  cost  per  passenger  handled  would  be  nearly 
doubled  by  doubling  the  number  of  trains.  If  at  the  same 
time  the  running  time  were  to  be  quickened  there  would 
be  a  still  further  increase  of  cost.  Largely  increased  total 
traffic  gives  the  only  opportunity  of  squaring  accounts. 

In  this  heavy  local  work  electric  traction  has  very 
great  advantages.  The  distances  are  usually  moderate, 
so  that  all  the  power  can  be  easily  distributed  from  one  or 
two  power  houses.  The  service  too,  is  so  dense  that  the 
station  can  be  kept  well  loaded  a  large  part  of  the  time,  and 
consequently  working  at  a  high  plant  efficiency.  Hence  the 
total  efficiency  of  the  power  supply  is  great,  while  the  abso- 
lute amount  of  power  required  is  considerably  less  with  elec- 
trics than  with  locomotives,  since  the  former  do  not  have 
to  carry  their  power  stations  upon  their  backs.  The  re- 
sults of  actual  competition  have  shown  the  desirability  of 
electric  working  for  suburban  passenger  traffic,  and  the 
character  of  the  service  to  be  given  is  tolerably  obvious. 
It  is  necessary  for  the  railway  company  to  take  advantage 
of  the  weak  points  of  its  competitors.  Electric  street  rail- 
ways have  the  advantage  in  the  matter  of  termini  and 
cover  their  field  thoroughly.  In  speed,  however,  they  are 
necessarily  somewhat  deficient  and  are  liable  to  blockades 
causing  very  annoying  delays. 

Hence  it  should  be  the  object  of  a  competing  railway 
by  running  frequent  trains  at  high  speeds  to  gain 
enough  time  for  its  passengers  amply  to  compensate  them 
for  the  time  lost  in  walking  at  the  ends  of  their  route. 
It  is  specially  necessary  to  retain  the  advantage  at  moder- 
ate distances,  say,  up  to  five  miles  from  the  center  of  the 
city,  for  here  the  competition  is  the  most  severe.  Fre- 
quent express  trains,  while  very  useful  in  extending  the 
exterior  service,  cannot  regain  the  traffic  lost  within  the 
effective  sphere  of  the  street  railway. 

The  electrical  problem  is  then  to  provide  frequent 
trains  capable  of  accommodating  one  or  two  hundred  people 


254   POWKR  DISTRIBUTION  FOR  ELECTRIC  RAILROADS. 

each,  running  at  a  speed  of  twenty-five  to  thirty-five  miles 
per  hour,  including  stops. 

In  the  present  state  of  the  art,  this  is  not  a  serious 
matter.     The  only  material  difficulties  that  have  been  met 
in  practice  are  those  connected  with  the  delivery  of  the 
necessary   current  to   the  moving  car,  and  these  are  no' 
now  of  much  moment. 

The  actual  amount  of  power  used  for  such  service  is 
easy  to  compute.     Taking  for  a  unit  a  train  composed  of 
one  long  motor  car  and  one  trail  car,  capable  together  o* 
accommodating  nearly  two  hundred  people,  we  can  derix 
the  necessary  power.     The  weight  of  the  two  cars  complete 
would   be   about   fifty   tons   of   which  about   thirty  tons 
would  belong  to  the  motor  car  and  twenty  to  the  trailef 
Allowing  for  ten  tons  live  load  the   total  weight  of  the 
loaded  train  is  sixty  tons. 

The  tractive  power  per  ton  may  be  taken  direct  fro' 
railway  practice  since  the  roadbed  and  rails  are,  or  alway 
should  be,  the  same  ordinarily  used  in  steam  railroading 

For  such  track  and  speed  the  tractive  coefficient  shou* 
never  be  more  than  12  Ibs.  to  15  Ibs.  per  ton.  Taking  tr  ^ 
latter  figure  as  covering  all  ordinary  contingencies  of  curves 
etc. ,  the  horizontal  effort  becomes  900  Ibs. ;  to  this  must  be 
added  the  air   resistance,  and  whatever  resistance  may  be 
due  to  grades.     At  thirty  miles  per  hour  the  air  resistance 
is  between  3  Ibs.  and  4  Ibs.  per  square  foot  of  surface  normal 
to  the  direction  of  motion. 

Allowing  200  Ibs.  for  this  factor  of  the  resistance  we 
have  a  horizontal  tractive  effort  of  uoo  Ibs.  and  there 
would  be  required  at  thirty  miles  per  hour  the  expenditure 
of  eighty-eight  mechanical  horse  power. 

Maintaining  this  speed  of  thirty  miles  per  hour  on 
grades,  the  additional  horse  power  required  would  be 
ninety-six  for  each  per  cent  of  grade,  or  dropping  the 
speed  to  twenty  miles  per  hour  on  the  grades,  sixty-four 
horse  power  for  each  per  cent  of  grade. 

Allowing  about  eighty  per  cent  net  efficiency  from 
the  motor  terminals  to  the  wheels  it  appears  that  the  elec- 


FAST   AND    HEAVY   RAILWAY   SERVICE. 


255 


trical  energy  to  be  delivered  to  our  unit  train  to  maintain 
a  uniform  speed  of  thirty  miles  per  hour  is  about  eighty 
to  eighty-five  kilowatts  per  train  on  a  level  track.  To 
maintain  a  thirty  mile  per  hour  schedule  under  ordinary 
conditions,  including  stops  and  the  net  effect  of  such  casual 
grades  as  might  generally  be  met  in  suburban  work,  might 
require  100  k.  w.,  but  the  mean  daily  output  per  train  in 
service  would  hardly  rise  above  the  original  figure  of  eighty 
to  eighty-five  kilowatts. 

During  crowded  hours  an  extra  trailer  would  often 
have  to  be  carried.   This  would  add  about  twenty-five  tons 


700 


500 


|400 


S300 


200 


100 


Street  Ry.Journal 


FIG.    124. 


to  the  weight  of  the  trains  and  would  call  for  about  thirty- 
six  additional  horse  power,  bringing  the  total  kilowatts  for 
the  train  up  to  nearly  120. 

This  estimate  of  power,  based  on  known  data  as  to  the 
weights  and  speed,  is  fully  borne  out  by  experiments  on 
trains  in  actual  operation. 

Figs.  124  and  125,  give  the  actual  power  taken  to  drive 
trains  of  five  and  three  cars  over  a  substantially  level  track 
at  approximately  thirty  miles  per  hour.  No  continuous 
records  of  speed  were  taken,  but  the  averages  were  about 
as  stated,  sufficiently  near  for  a  fair  comparison.  Fig.  124  is 
the  record  of  a  run  with  a  train  consisting  of  a  motor  car 
and  four  trailers  weighing,  with  a  moderate  load  of  pas- 
sengers, very  nearly  122.5  tons,  a  trifle  more  than  double 
the  weight  of  our  assumed  standard  train.  The  average 


256     POWER   DISTRIBUTION   FOR   ELECTRIC    RAILROADS. 

voltage  was  530  and  the  average  amperes  are  very  nearly 
290,  or  1 54k.  w.  Since  the  air  resistance  for  four  cars 
is  but  a  trifle  more  than  for  two,  the  close  agreement 
of  this  run  with  our  estimate  is  obvious. 

Fig.  125  shows  a  run  with  one  motor  car  and  two  trailers 
weighing  with  the  passengers  89. 5  tons;  speed  about  the 
same  as  in  Fig.  124  and  average  voltage  475.  The  average 
current  appears  to  be  about  230  amperes,  giving  109  k.  w. 
total  output,  which  again,  reduced  to  a  two-car,  sixty-ton 
basis  gives  in  the  vicinity  of  eighty  kilowatts  for  the  nor- 
mal train.  Another  run  over  the  same  track  as  in  Fig.  125 


coo 

500 
«400 
0,300 

e 

^200 
100 
n 

h 

\ 

i\ 

K 

Xt*»« 

\j 

\ 

\ 

N 

N 

\ 

^ 

'  \ 

/N 

I 

FIG.    125. 

with  a  three-car  train  two  tons  lighter,  and  in  the  opposite 
direction  showed  an  average  power  consumption  of  125  k. 
w.  The  same  motor  car  was  used  in  all  three  tests.  The 
sudden  increases  in  the  current  were  mainly  due  to  sudden 
changes  at  the  controlling  apparatus  causing  rapid  accelera- 
tion. These  very  large  momentary  currents  are,  of  course, 
undesirable  and  can  be  much  reduced  by  careful  handling 
and  better  adjustment  of  the  controller  to  its  work. 

The  normal  average  current  for  such  a  train  at  500 
volts  would  then  be  not  far  from  1 60  amperes.  With  a 
working  voltage  of  about  600  at  the  motors,  which  is  a 
desirable  arrangement,  about  135  amperes  would  be  re- 
quired. One  would  not  go  far  wrong,  then,  in  taking  for 
ordinary  cases  200  amperes  as  about  the  largest  average 
which  would  be  called  for  by  any  one  train,  allowing  the 
use  of  two  trailers  when  convenient.  The  ordinary  loaded 


FAST  AND   HEAVY   RAILWAY  SERVICE. 


257 


train  would  average  135  to  160  amperes,  according  to  the 
voltage. 

The  experience  of  the  past  two  years  on  the  Nantas- 


i    1    * 


ket  Beach  line  has  added  materially  to  our  knowledge  of 
electric  railway  work  of  the  larger  sort.  Fig.  126  shows 
in  detail  the  result  of  one  of  the  experimental  runs  over 
the  entire  length  of  the  road,  10.5  miles.  The  train  con- 


258    IOWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

sisted  of  a  motor  car  weighing  32  tons  and  a  trailer  weigh- 
ing 28  tons.  Both  were  mounted  on  double  trucks  with 
36  in.  wheels,  and  the  former  was  equipped  with  two  125 
h.  p.  motors,  geared,  with  a  speed  reduction  of  1.45  to  i, 
to  the  axles  of  the  same  truck.  The  diagram  shows  the 
speed,  amperes,  volts,  watt-hours  and  time,  together  with 
the  curves  and  profile  of  the  road.  The  power  required 
at  an  average  speed  of  29.6  miles  per  hour  was  87.89  k.w. 
equivalent,  taking  account  of  the  motor  efficiency  at  this 
particular  output,  to  about  90  mechanical  horse  power. 

A  service  run  with  the  same  train  weighing  with  its 
passengers  64  tons,  at  an  average  speed  of  1 7  miles  per 
hour,  including  twelve  stops  at  intermediate  stations,  re- 
quited an  average  output  of  65.2  k.w.  In  this  case  the 
severe  work  of  acceleration,  due  to  the  numerous  stops,  is 
very  evident. 

In  these  and  many  other  runs  on  which  careful  meas- 
urements were  made,  one  singular  fact  regarding  the  train 
resistances  was  noted,  which  has  an  important  bearing 
on  railway  work. 

The  output  required  for  a  motor  car  alone  was  not 
greatly  increased,  for  the  same  speed,  by  the  addition  of  a 
trailer.  Even  two  or  three  trailers  produced  a  dispropor- 
tionately small  increase.  The  apparent  decrease  of  the 
tonnage  coefficient  on  long  trians  has  been  well  known  in 
general  railway  work,  but  the  ease  of  exact  measurements 
makes  it  particularly  striking  in  the  case  in  hand.  Of 
course  even  here  the  varying  conditions  of  track,  load, 
speed,  acceleration  and  wind  produce  somewhat  divergent 
results,  but  the  same  general  fact  is  apparent  throughout. 

The  apparent  power  required  per  ton  is  much  greater 
for  the  motor  car  than  for  those  forming  the  train.  The 
following  table  shows  the  approximate  results  obtained  at 
several  different  speeds  and  under  various  conditions,  in 
kilowatts  per  ton. 

The  reduction  for  air  resistance  is  made  by  the  data 
from  Fig.  135.  The  value  of  this  resistance  has  been  so 
thoroughly  determined  for  these  very  moderate  speeds 


FAST   AND   HEAVY   RAILWAY  SERVICE. 


259 


SPEED—  MILES    PER    HOUR. 

14* 

17** 

30 

40 

2.8 

1.44 

2.2 

2.O 

Motor  car  less  air  pressure. 

2-5 

1.14 

I.4I 

I.O 

One  trailer  

0.71 

0-55 

0.46 

0-5 

Two  trailers  

0.85 

0.66 

Pour  trailers.  .  .      

0-53 

*  Heavy  acceleration.              **  Service  run. 

that  the  above  results  can  hardly  be  materially  in  error. 
Even  taking  into  account  the  uncertainty  introduced  by 
the  wind  and  gear  friction,  the  above  results,  particularly 
those  at  low  speeds,  show  clearly  enough  that  we  are  here 
dealing  with  differences  of  resistance  other  than  those  pro- 
duced by  air  pressure. 

It  is  altogether  probable  that  the  tractive  resistance  of 
the  driving  wheels  is  materially  greater  than  the  pure 
rolling  friction  of  the  other  trucks.  This  is  assuredly  the 
case  if  there  is  any  tendency  to  slip,  and  near  the  limit  of 
adhesion  the  effect  must  become  very  noticeable,  which 
would  produce  an  apparent  increase  of  tonnage  coefficient 
with  trains  above  a  certain  length  and  weight.  Under 
even  ordinary  conditions  there  must  exist  a  certain  grind- 
ing friction  of  the  driving  wheels,  much  larger,  to  judge 
from  the  data  at  hand,  than  ordinary  rolling  friction,  per- 
haps twice  as  great.  A  similar  condition  is  thought  by 
many  engineers  to  hold  with  respect  to  locomotive  driving 
wheels. 

The  matter  is  important  since  it  indicates  great  ad- 
vantage in  employing  trains  rather  than  the  single  cars 
which  have  often  been  advocated  for  electric  service  on 
a  large  scale. 


260     POWER   DISTRIBUTION   FOR    ELECTRIC   RAILROADS. 

The  Nantasket  experiments  also  afford  valuable  data 
with  respect  to  the  power  required  for  acceleration.  They 
are  fairly  concordant  and  show,  for  a  60  ton  two  car  train, 
that  acceleration  from  rest  to  25  miles  per  hour  in  one 
minute,  requires  an  aggregate  expenditure  of  just  about 
2  k.  w.  h.,  /'.  e.  about  120  k.  w.  average  output. 

This  gives  an  experimental  basis  for  computing  the 
power  required  by  a  train  making  frequent  stops,  as  in 
suburban  service  on  steam  railways.  We  shall  calculate  a 
case  of  this  kind  later.  The  important  fact  to  note  con- 
cerning such  service  is  the  very  severe  acceleration  due  to 
the  short  runs  between  stations  and  the  high  maximum 
speeds  that  must  be  reached.  With  stops  every  mile  or 
mile  and  a  half  this  maximum  has  to  be  something  like 
twice  the  average  speed  including  stops,  and  can  only  be 
maintained  for  a  fraction  of  a  minute,  after  which  the 
brakes  have  to  be  applied.  For  example,  if  the  stations 
are  a  mile  and  a  half  apart  and  the  running  speed  is  to  be 
30  miles  per  hour,  the  maximum  speed  must  be  50  to  60 
miles  per  hour  and  it  must  be  reached  in  one  minute  or 
less.  This  would,  for  a  60  ton  train,  demand  during  ac- 
celeration an  average  of  250  to  300  k.  w.  The  nearer 
together  the  stations  the  more  severe  becomes  the  work 
of  acceleration  due  to  a  given  schedule  of  speed.  With 
stations  as  near  together  as  they  have  to  be  in  some  ele- 
vated service  the  tremendous  drawbar  pulls  are  likely  to 
come  near  to  the  limit  of  adhesion  if  a  single  motor  car 
be  used  and  there  is  then  considerable  to  be  said  in  favor 
of  making  every  car  a  motor  car,  in  spite  of  the  loss  of 
efficiency.  Where  certain  work  must  be  done  as  part 
of  the  necessary  traffic  scheme  the  method  that  accom- 
plishes it  need  not  be  too  closely  scrutinized.  Single 
cars  or  trains  with  many  motors  quite  certainly  take 
considerably  more  power  to  drive  at  speed  than  ordinary 
trains  of  the  same  capacity  and  the  advisability  of  using 
one  or  the  other  is  purely  a  question  of  local  traffic  con- 
ditions. Each  case  of  this  kind  must  stand  on  its  own 
merits,  with  the  presumption  rather  in  favor  of  ordinary 


FAST   AND    HEAVY   RAILWAY   SERVICE.  26 1 

train  practice  until  it  is  shown  to  be  inadequate  under  the 
conditions  imposed.  On  the  other  hand  if  one  is  compelled 
to  resort  to  very  extreme  work  of  acceleration  it  is  more 
economical  of  power  to  accelerate  very  quickly  and  then 
coast  than  to  accelerate  more  slowly  and  cut  off  current 
only  to  put  on  the  brakes. 

In  starting,  during  certain  periods  of  acceleration  and 
on  grades,  much  more  current  is  required.  From  Fig.  125 
we  may  judge  that  the  current,  even  at  600  volts  working 
pressure,  might  well  rise  to  400-500  amperes,  while  to 
maintain  schedule  on  a  grade  of,  say,  two  or  three  per  cent 
would  demand  fully  as  much.  Altogether  the  maximum 
working  current  per  train  must  be  taken  as  high  as  500 
amperes,  although  this  amount  would  be  seldom  called  for. 


FIG.  127. 

The  supply  of  so  great  a  current  to  the  moving  train  is 
not  altogether  a  simple  matter,  and  has  involved  consider- 
able experimentation. 

The  ordinary  street  car  trolley  burns  badly  with  such 
currents,  and  special  wheels  arranged  to  secure  extra  large 
contact  with  the  trolley  wire  are  needful,  while  sometimes 
two  independent  trolleys  have  helped  the  matter. 

The  trolley  wire  itself  is  necessarily  of  large  cross  sec- 
tion, so  large  as  to  involve  some  trouble  in  support,  and 
several  unusual  shapes  have  been  tried  to  improve  the  con- 
tact area  and  facilitate  suspension.  Fig.  127  shows  three 
such  forms,  the  simpler  of  which  is  in  use  on  a  portion  of 
the  Nantasket  Beach  electric  road,  the  Cleveland  &  L,orain 
Railway  and  the  Boston  Subway.  Neither  shape  of  the 
right  hand  pair  is  unobjectionable,  though  both  give  a  good 


262     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

opportunity  for  gripping  the  wire  firmly  in  the  clamps  with- 
out forming  projections  which  would  be  likely  to  throw  off 
the  trolley  when  running  at  high  speed.  Both  are  likely  to 
give  trouble  from  twisting,  so  as  to  make  poor  contact  with 
the  trolley  wheel.  The  more  nearly  circular  the  cross  sec- 
tion of  the  wire  can  be  made,  while  still  permitting  projec- 
tions or  grooves  for  gripping,  the  more  smoothly  the  trolley 
will  run  and  the  better  for  general  contact.  A  plain  round 
wire  would  be  the  best  if  it  could  be  clamped  so  as  not  to 
produce  projections  to  cause  trouble  at  high  speed.  A 
grooved  round  wire  with  special  clamps  has  recently  been 
introduced  with  good  results.  It  appears  at  the  left  in 
Fig.  127.  Of  the  two  pioneer  heavy  service  roads,  one, 
the  Nantasket,  uses  the  two-lobed  trolley  wire  shown  in 
Fig.  127,  weighing  one  pound  per  linear  foot,  the  other, 
the  Mt.  Holly  branch  of  the  Pennsylvania  Railroad,  took 
for  its  rather  lighter  service  a  No.  oo  plain  wire. 

900000  c.  m.  900000  c.  m. 


750000  c.  m.                     \  /                  750000  c.  m. 

1   1    1    |    1    1    1    1                             ^Y                            |    1    1    1    |    1    1    1 

\    a 

b           c            d           e    [Cj  /           g            h           i            j      E 

Street  Rj.Jourual 

FIG.  128. 

To  get  a  clear  idea  of  the  power  requirements  on  this 
class  of  road  let  us  assume  a  fairly  simple  case  and  work 
out  the  feeder  system.  Let  A  B  (Fig.  128)  be  a  straight 
suburban  system,  50,000  ft.  (nearly  10  miles)  in  length, 
with  no  grades  steeper  than  ^  per  cent,  double  tracked 
throughout  with  stations,  say,  every  5000  ft.  Let  the 
power  station  be  at  C,  the  middle  point,  which  would  gen- 
erally be  as  convenient  as  anywhere.  We  will  assume 
trains  to  be  run  on  ten  minute's  headway,  and  to  make  the 
round  trip  in  an  hour.  During  the  busy  hours,  7-10  A.M. 
and  4-7  P.M.  ,  the  trains  should  consist  of  motor  car  and  two 
trailers,  at  other  times  of  motor  car  and  a  single  trailer. 
Certain  trains  would  probably  have  to  carry  three  trailers. 
From  8  P.M.  on,  and  before  7  A.M.  twenty  minute  headway 
would  be  sufficient.  During  the  busy  hours  there  would 


FAST  AND   HEAVY  RAILWAY  SERVICE.  263 

then  be  twelve  trains  in  service,  six  of  them  heavily 
loaded,  and  each  a  three-car  train.  From  the  rush  hours 
on  the  number  of  trains  would  be  the  same  as  before,  until 
8  P.M.,  after  which  six  trains  would  suffice. 

From  these  data  we  may  calculate  the  power  which 
would  have  to  be  delivered.  As  in  other  railway  work  the 
feeding  system  is  really  determined  by  the  conditions  of 
maximum  load.  This  would  usually  fall  between  8  and  9 
A.M.  during  which  period  six  trains  would  be  in  service 
on  each  half  of  the  line.  Of  these  the  outgoing  trains 
would  be  nearly  empty,  but  on  the  other  hand  all  the  in- 
going trains  would  be  crowded,  and  one  or  two  of  them 
would  carry  an  extra  car.  We  must,  therefore,  allow  for 
extra  load,  and  a  fair  assumption  would  be  to  consider  all 
the  trains  as  three-car  trains  well  loaded.  This  means  not 
far  from  120  k.  w.  per  train,  about  1440  k.  w.  for  the  full 
output  of  the  station. 

The  working  voltage  should  be  as  high  as  feasible. 
Without  any  radical  innovations  it  is  quite  practicable  ta 
allow  a  normal  voltage  of  600  at  the  motors.  This  should 
not  be  much  exceeded,  while  the  pressure  may  without 
trouble  be  allowed  to  fall  ten  per  cent  below  this  at  the 
termini  during  heavy  loads.  Let  us  first  examine  the  ter- 
minal conditions.  Two  trains  will  ordinarily  be  handled 
in  that  region,  requiring  by  our  assumption  240  k.  w.  To 
allow  for  rapid  acceleration  of  a  heavy  train,  fully  this 
amount  of  power  may  be  temporarily  required,  but  two 
trains  will  not  have  to  start  together.  If,  following  Fig.  119, 
we  allow  500  amperes  available  at  the  terminus  we  shall  be 
safe  so  far  as  this  point  is  concerned. 

As  to  drop,  if  we  take  ten  per  cent  as  average  during 
the  busy  hours  we  shall  not  go  far  wrong,  allowing  twenty 
per  cent  at  the  termini  during  heavy  loads.  Even  a  little 
more  would  be  safe  if  occasion  demanded,  so  that  if  the 
dynamos  gave  about  600  volts  overcompounded  about  ten 
per  cent,  say,  to  670,  the  minimum  pressure  could  be  safely 
taken  down  150  volts  to  520.  We  must  then  have  at  the 
termini  enough  feeder  capacity  to  give  500  amperes  with- 
out dropping  the  voltage  below  520. 


264    POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

Now  for  such  a  road  as  we  are  considering  the  track 
should  be  first  class,  rails  not  less  than  eighty  pounds  per 
yard,  and  most  carefully  bonded.  Four  lines  of  eighty 
pound  rails  give  an  equivalent  conductivity  of  about  5, 120,- 
ooo  c.  m.  Assuming  that  the  bonding  lowers  the  con- 
ductivity one- third,  the  track  is  equivalent  to  about 
3,400,000  c.  m.  of  copper.  In  spite  of  this  the  heavy 
service  makes  it  necessary  to  take,  say,  14  as  the  track 
constant. 

Now  turning  to  Plate  II  (p.  81)  we  can  find  the  feeder 
area.  It  is  700,000  c.  m.  per  one  hundred  amperes  for  fifty 
volts  drop.  In  our  case  then  the  feeder  area  is 

700,000  X  5 

—  =  1,166,000. 

3 

This  feeder  should  supply  the  terminal  sections  of  track, 
say,  5000  ft.  long.  For  convenience  we  may  divide  the 
line  into  5000  ft.  sections  lettered  on  Fig.  122.  Sections  # 
(and/)  being  thus  disposed  of,  we  may  turn  to  sections  b 
and  c.  treating  them  together.  The  average  distance  of 
transmission  is  15,000  ft.  and  the  maximum  load  may  be 
taken  as  one  train  under  full  headway  and  one  starting, 
say,  650  amperes.  From  Plate  II  the  copper  is 
400.000  X  6  5==866>ooocm 

3 
Similarly,  for  sections  d  and  e  we  have  approximately 

140,000  x  6.5  = 

o 
Now  for  the  working  conductors  and  then  to  fine  down  the 

feeders. 

Using  trolley  wire  such  as  is  used  on  the  Nantasket 
Beach  road,  we  should  have  about  660,000  c.  m.  available 
at  once  in  the  two  trolley  wires.  Much  smaller  trolley  wire 
would  be  inadvisable  on  account  of  lack  of  contact  surface 
and  carrying  power.  Sections  d  and  e  will  obviously  take 
care  of  themselves  and  generally  have  large  capacity  to 
spare.  Along  b  and  c  the  trolley  wire  is  available,  and  even 
if  the  maximum  load  were  at  the  further  end  of  b  a  750,000 
c.  m.  feeder  extended  from*:  along  these  sections  would  give 


FAST   AND   HEAVY   RAILWAY   SERVICE.  265 

sufficient  conductivity.  Now  for  the  terminal  sections. 
Throughout  a  the  660,000  c.  m.  of  the  trolley  wires  is 
available.  Hence  up  to  the  beginning  of  the  section 
1,000,000  c.  m.  is  sufficient  without  allowance  for  help 
from  the  other  feeder.  Just  how  much  this  help  would  be 
is  hard  to  estimate.  It  should  certainly  not  be  less  than 
100,000  c.  m.  If  then  the  long  feeders  are  of  900,000 c.  m., 
the  maximum  load  conditions  for  the  road  as  a  whole  will 
be  properly  met.  We  may  now  count  up  the  copper  as 
follows: 

Ft.  Lbs. 

Trolley  wire  100,000  100,000 

750,000  c.  m.  40,000  90,000 

900,0000.  m.  50,000  135,000 


Total          325,000 

This  copper  would  cost  in  ronnd  numbers  $50,000,  and  in 
place,  including  the  pole  line,  nearly  or  quite  $60,000.  At 
average  load  during  busy  hours,  say,  1800  amperes  total, 
the  loss  would  not  be  far  from  ten  per  cent,  while  the  aver- 
age loss  for  the  all-day  run  would  be  considerably  smaller. 
But  this  is  not  the  last  word  on  the  working  conductor 
question  by  any  means.  A  daring  and  apparently  highly 
successful  experiment  has  been  carried  out  on  a  new  section 
of  the  Nantasket  Beach  line  3^  miles  long,  which  promises 
good  results  on  a  larger  scale.  It  consists  of  the  applica- 
tion of  third  rail  supply  to  the  service  track  of  a  steam 
railroad.  The  line  thus  changed  was  that  section  of  the 
Plymouth  division  of  the  New  York,  New  Haven  &  Hart- 
ford Railroad,  lying  between  East  Wey mouth  and  Nan- 
tasket Junction.  An  insulated  steel  rail  was  placed  mid- 
way between  the  track  rails  and  made  to  serve  as  the 
working  conductor.  Current  is  taken  from  this  rail  by 
means  of  a  soft  cast  iron  shoe  carried  beneath  each  of  the 
trucks.  The  third  rail  is  laid  in  thirty  foot  lengths,  each 
supported  by  four  ash  blocks,  saturated  with  insulating 
compound  by  treatment  in  vacuum  pans.  These  blocks 
are  so  let  into  the  ties  that  the  surface  of  the  third  rail  is 
one  inch  above  the  track  rail.  The  third  rail  is  bonded 


J66   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

with  two  heavy  copper  bonds  at  each  joint,  and  where 
there  are  crossings  the  rail  is  omitted  and  the  cars  pass 
over  on  momentum.  The  rail  is  made  continuous  electri- 
cally over  the  crossings  by  a  buried  lead  covered  cable,  and 
a  sloping  leading-block  of  hard  wood  is  spiked  to  the  ties 
at  each  side  of  the  crossing  to  prevent  shock  to  the  shoes. 
The  arrangement  of  the  third  rail  and  the  contact  shoe  is 
shown  in  section  by  Fig.  129,  and  an  elevation  of  a  single 
shoe  in  Fig.  130. 

The  supply  rail  weighs  ninety-four  pounds  per  yard 


FIGS.  129  AND  130. 

and  is  of  rather  odd  shape,  to  secure  sufficient  weight 
without  making  the  rail  too  high,  and  to  shelter  the  in- 
sulating blocks.  The  shoes  are  a  little  more  than  one  rail 
length  apart,  and  are  supported,  as  shown  in  Fig.  130,  by 
a  double  toggle  joint  having  a  rather  limited  play.  The 
weight  of  the  shoe,  about  twenty  pounds,  is  enough  to 
give  good  contact. ' 

The  return  circuit  is,  of  course,  through  the  track 
rails,  which  weigh  about  ninety  pounds  per  yard,  and  are 
thoroughly  bonded  with  short  lengths  of  copper  cable.  As 
a  matter  of  fact,  during  some  weeks  of  successful  operation 


FAST   AND    HKAYY   RAILWAY   SERVICE. 


267 


the  bonding  was  incomplete,  and  contact  was  furnished  by 
the  fishplates  at  many  of  the  joints.  The  system  has  now 
been  working  several  seasons  with  entire  success.  The 
cars,  which  run  over  the  entire  Nantasket  Beach  road,  are, 
of  course,  equipped  with  an  overhead  trolley  as  well  as  with 
the  contact  shoes,  and  from  Nantasket  Junction  to  the 


FIG.  131. 

Pemberton  terminus  the  overhead  trolley  line  is  in  use. 
The  character  of  the  overhead  structure  in  this  part  of 
the  line  is  well  shown  in  Fig.  131.  The  greater  neatness 
and  simplicity  of  the  third  rail  arrangement  is  obvious. 
Until  this  experiment  fear  of  serious  leakage  has  deterred 
engineers  from  using  such  construction  on  ordinary  road- 
beds. A  regular  railroad  construction  with  rails  carried 
on  ties  slightly  above  the  surface  of  .the  ground  is  very 


268     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

much  less  liable  to  leakage  than  street  railway  construc- 
tion with  nearly  buried  rails,  particularly  since  in  the 
former  the  third  rail  can  be  supported  on  adequate  insu- 
lators. 

Besides  this,  an  amount  of  leakage  which  would  be 
formidable  in  street  railway  work  may  be  relatively  quite 
small  in  the  heavy  service  of  a  suburban  line.  The  third 
rail  has  about  700  insulators  per  mile,  and  if  they  are  of 
tolerably  good  material,  the  leakage  current  must  neces- 
sarily be  small  even  in  very  wet  weather.  Tests  show  that 
this  is  so.  In  ordinary  weather  the  leakage  is  not  serious, 
and  under  the  worst  conditions  it  still  leaves  the  system 
in  good  operative  condition.  This  might  be  expected,  for 
it  is  certainly  a  poor  insulator  that,  even  when  damp  on 
the  surface,  would  let  pass  any  considerable  current  under 
a  pressure  of  600  volts.  If  the  track  is  not  actually  sub- 
merged, the  insulation  should  remain  fairly  high  if  the 
insulators  do  not  deteriorate.  Snow  is  a  rather  good  in- 
sulator, and  if  the  roadbed  is  well  drained,  even  melting 
snow  will  not  cause  much  inconvenience. 

Such  a  third  rail  structure  generally  renders  feeders 
quite  needless.  For  a  road  such  as  we  have  been  investi- 
gating a  one  hundred  pound  supply  rail  on  each  track  would 
give,  when  well  bonded,  a  total  equivalent  conductivity  of 
just  about  2,130,000  c.m.,  allowing  one-third  of  the  total 
resistance  to  be  in  the  bonding.  This  is  almost  precisely 
the  equivalent  of  the  available  copper  shown  in  Fig.  128. 
On  a  longer  road,  or  with  heavier  service,  supplementary 
feeders  would  be  necessary. 

The  cost  of  this  third  rail  system  is  decidedly  low.  A 
one-hundred  pound  rail  weighs  eighty-eight  tons  per  mile, 
costing  at  present  prices  not  far  from  $2300.  Insulators, 
placing  and  bonding  should  not  exceed  $700  per  mile  addi- 
tional. On  this  basis  the  third  rail  system  can  be  installed 
rather  more  cheaply  than  the  overhead  system  and  is  far 
simpler  to  maintain  and  operate. 

A  sectionalized  third  rail  has  been  more  than  once 
suggested  as  a  remedy  for  leakage.  Whatever  may  be  its 


FAST  AND   HEAVY   RAILWAY  SERVICE.  269 

merits  for  street  work,  it  is  disadvantageous  in  that  it 
virtually  throws  away  the  immense  conductivity  of  the 
supply  rail  and  thus  greatly  increases  the  first  cost  of  the 
line.  A  fraction  of  the  extra  expense  applied  to  careful 
drainage  of  the  roadbed  and  good  insulation  would  render 
sectionalization  needless  for  this  particular  kind  of  work. 

A  copper  third  rail  deserves  consideration  in  connec- 
tion with  this  class  of  work  on  account  of  its  great  con- 
venience in  the  matter  of  insulation,  ease  of  placing,  and 
elimination  of  the  bonding  difficulty.  Its  net  cost  is  rather 
more  than  that  of  a  steel  third  rail. 

The  third  rail  section  of  the  Nantasket  line  has  now 
been  installed  about  three  years  and  although  it  has  not 
been  in  operation  during  the  winter,  when  the  most  trying 
weather  conditions  would  have  been  encountered,  the  re- 
sults have  on  the  whole  been  so  satisfactory  that  the  rail- 
way company  has  equipped  another  of  its  lines  in  a  singular 
manner.  This  is  a  line  extending  from  Hartford  to  Ber- 
lin, Conn.,  via  New  Britain,  a  distance  of  12.3  miles. 

The  arrangement  of  the  conducting  rail  is  substan- 
tially that  shown  in  Fig.  130.  The  lower  edges  of  the 
rail  are  little  more  than  i^in.  above  the  ties  and  the  road 
is  operated  throughout  the  winter  thus  furnishing  a  crucial 
test  of  the  insulation.  Since  the  construction  of  this 
Hartford-New  Britain  line  it  has  been  extended  beyond 
New  Britain  to  Bristol  a  distance  of  8.8  miles  and  be- 
tween New  Britain  and  Berlin  2.5  miles.  The  Nantas- 
ket Beach  road  has  also  been  extended  from  East  Wey- 
mouth  to  Braintree  4.4  miles.  These  additions  after  a  year 
or  two  of  experience  are  strong  evidence  of  the  operative 
qualities  of  the  third  rail  system,  which  is  used  throughout. 
Still  another  branch  line  of  the  N.  Y.,  N.  H.  &  H.  R.  R. 
has  been  transmuted  into  an  electric  road  with  others  to 
follow.  The  branch  referred  to  is  that  from  Stamford  to 
New  Canaan,  Conn.,  8  miles  long.  Here  the  overhead 
trolley  is  used  to  facilitate  exchange  of  traffic  with  the 
Stamford  street  railway  if  convenient.  The  trolley  wire 
is  No.  ooo  and  No.  oooo  and  there  has  oeen  no  trouble  in 


270   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

getting  adequate  contact.  The  bonding  on  this  and  simi- 
lar lines  is  worth  noting  as  it  seems  to  be  especially  good. 
At  each  joint  are  applied  a  pair  of  "  Crown  "  bonds  of  the 
general  type  shown  in  Chap.  II.  both  of  leaf  copper  pro- 
portioned and  arranged  as  shown  in  Fig.  132.  This  bond- 
ing is  applied  under  the  base  of  the  rails,  the  terminals 
being  forced  upwards  into  holes  drilled  in  the  base  and  the 
drift  pins  being  squeezed  up  into  place  by  a  special  tool. 


Street  Ry.  Journal 


FIG.  132. 


The  countersunk  bond  terminals  are  then  set  up  with  a 
hammer  so  that  the  pins  cannot  work  loose. 

Another  ingenious  innovation  in  this  road  is  found  in 
the  motor  trucks.  Each  of  these  is  fitted  with  two  175 
h.  p.  motors  which  are  carried  by  and  suspended  to  a 
truck  frame  independent  of  the  car  truck  proper  which 
rests  upon  it  at  the  boxes.  Thus  the  whole  upper  part  of 
the  truck  is  removable  leaving  the  working  parts  freely 
accessible. 

The  wooden  insulating  blocks  used  at  Nantasket  have 
been,  so  far,  fairly  successful  and  have  kept  the  leakage, 
under  ordinary  conditions,  down  to  a  rather  small  amount. 
The  insulators,  however,  have  in  some  cases  shown  marked 
deterioration  and  it  is  the  writer's  belief  that  the  leakage 
will  become  serious  if  the  use  of  wood  is  long  continued. 
Insulators  so  short  and  presenting  so  great  surface  as 


FAST  AND   HEAVY   RAILWAY  SERVICE.  271 

these  should  be  of  porcelain  if  they  are  to  have  and  main- 
tain insulating  properties  such  as  the  conditions  demand. 

On  these  lines  it  was  necessary  to  keep  the  third  rail 
close  to  the  ties  in  order  to  avoid  striking  the  fireboxes  of 
locomotives  occasionally  used  on  the  same  tracks,  but  this 
proximity  is  certain  to  produce  some  disagreeable  results 
unless  insulation  is  more  carefully  carried  out  than  it  is  at 
present. 

Moreover  the  third  rail  is"  in  no  way  protected  from 
accidental  contact  of  any  kind,  and  while  the  voltage  em- 
ployed, 600  to  700  volts,  cannot  be  condemned  as  highly 
dangerous  to  life  it  is  yet  certainly  beyond  the  danger 
line,  and  can  unquestionably  produce  grave  shocks  and 
death.  At  least  one  man  has  been  killed  on  these  circuits 
and  others  have  been  injured.  It  is  not  putting  the  facts 
too  strongly  to  say  that  to  continue  the  use  of  an  un- 
guarded third  rail  on  surface  roads  approaches  criminal 
negligence.  Aside  from  this  question  of  danger  short 
circuits  are  very  easily  produced  on  an  unguarded  third 
rail  and  consideration  of  public  safety  and  private  conven- 
ience alike  demand  the  suppression  of  so  dangerous  a 
practice. 

The  facts  regarding  the  leakage  encountered  on  these 
third  rail  systems  have  never  been  made  public.  That 
there  is  at  times  heavy  leakage  admits  of  little  doubt,  but 
the  roads  have  continued  operative  under  rather  trying 
conditions  in  spite  of  it.  The  insulation  used  seems, 
however,  inadequate  and  should  be  assiduously  shunned 
in  future  work  along  this  line. 

Nevertheless  we  have  in  the  third  rail  system  a  very 
important  addition  to  the  methods  of  electrical  traction, 
and  one  that  is  capable  of  being  developed  far  beyond  any 
point  which  has  yet  been  attained.  The  use  of  proper 
insulators  and  the  allowance  of  sufficient  clearance  under 
the  third  rail  will  lead  to  greatly  improved  results,  and  in 
the  last  resort  careful  construction  and  drainage  of  the 
roadbed  will  prove  immensely  helpful. 

When  the  method  has  been  thoroughly  worked  out 


272    POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

it  promises  to  be  of  very  great  value  in  many  cases  of 
heavy  traction,  for  it  is  cheap,  simple,  easy  to  apply  and 
gives  what  most  other  systems  conspicuously  lack,  an 
adequate  contact  area  on  the  working  conductor.  The 
greatest  difficulties  yet  apparent  in  the  third  rail  working 
are  the  troubles  due  to  sleet  and  to  failure  of  the  bonding. 
In  sleet  and  ice  a  coating  of  the  rails  is  supplied  that  is, 
so  far,  almost  impossible  to  cut  through  enough  to  get 
good  contact,  and  under  these  circumstances  the  third 
rail  lines  are  sometimes  driven  back  to  steam  locomotives. 
It  should  not  be  impossible  to  devise  means  of  cutting 
through  the  sleet  successfully,  but  thus  far  the  difficulty 
has  been  formidable. 

Even  the  thorough  system  of  bonding  employed  gives 
considerable  trouble  from  the  gradual  breaking  of  bonds 
under  the  stress  of  continual  shocks  at  the  joints.  The 
center  third  rail  is  particularly  bad  in  this  respect,  as  it 
takes  up  the  space  in  the  middle  of  the  track  so  as  to 
make  proper  surfacing  and  tamping  of  the  roadbed  ex- 
tremely difficult.  A  side  third  rail  would  be  far  easier  to 
keep  up  in  this  respect.  As  to  bonds  the  writer  is  in- 
clined to  think  that  very  flexible  cable  bonds  with  the 
terminals  electrically  welded  to  the  rail  would  give  relief 
from  the  present  situation.  At  all  events  it  is  well  worth 
trying. 

One  of  the  standard  open  cars  of  the  Nantasket  Beach 
line  is  shown  in  Fig.  133.  Bach  has  sixteen  seats  and  will 
accommodate  fully  one  hundred  passengers.  Sixteen  of 
these  are  fitted  up  as  motor  cars  and  similar  cars  are  used 
as  trailers.  Each  motor  car  is  fitted  with  two  G.  E.  2000 
motors  of  the  type  shown  in  Fig.  134  arranged  for  series- 
parallel  control.  The  cars  are  fitted  with  air  brakes  and  air 
whistle,  the  air  being  pumped  into  a  tank  by  a  motor  auto- 
matically controlled  by  the  pressure.  The  motors  are  good 
for  over  a  hundred  horse  power  each  at  full  field,  and  on  the 
straight  level  stretch  in  the  middle  of  the  Nantasket  Beach 
line  a  speed  of  more  than  seventy  miles  per  hour  has  been 
reached.  At  such  a  speed  the  motion  is  quite  smooth  and 


FAST  AND   HEAVY   RAILWAY  SERVICE. 


273 


the  great  speed  cannot  be  realized  except  by  timing  the 
car.  The  normal  speed  is  from  twenty  to  thirty  miles  per 
hour  in  regular  service,  and  the  system  has  proved  entirely 
reliable. 

For  this  heavy  special  or  suburban  service  electric 
power  is  singularly  well  suited.  It  does  the  work  well,  at 
high  efficiency  and  at  moderate  cost.  Basing  an  estimate 
of  cost  on  a  normal  two-car  train,  requiring  eighty  kilowatts 


FIG.    133. 

while  running  and  allowing  for  this  eighty  kilowatts  average 
output  at  the  station,  we  can  figure  readily  the  cost  of 
power  per  train  mile.  The  train  makes  an  average  of 
about  twenty  miles  per  hour.  It  thus  demands  four  kilo- 
watt, hours  per  train  mile.  The  service  is  twenty  hours  per 
day,  and  the  average  load  fairly  high,  probably  more  than 
half  the  maximum.  On  this  basis  the  power  per  train  mile 
should  not  cost,  delivered  on  the  line  at  the  station,  more 
than  six  cents,  including  station  charges  of  every  sort  and 
kind.  Two  cents  additional  should  cover  all  charges  for 
the  delivery  of  the  power,  including  the  motors.  Even. 


274     POWER   DISTRIBUTION    FOR   ELECTRIC    RAILROADS. 

more  unfavorable  conditions  than  those  assumed  would 
generally  leave  the  power  charge  per  train  mile  at  not  over 
ten  cents.  This  is,  of  course,  relatively  very  much  better 
than  street  railway  practice,  but  the  units  are  far  larger, 
the  service  easier  in  every  way,  the  grades  smaller  and  the 
work  far  more  controllable  and  regular. 

By  far  the  most  interesting  line  of  advance  in  electric 
railway  work  is  toward  long  distances  at  very  high  speeds. 
The  idea  of  clipping  the  wings  of  Time  by  doubling  our 
present  railway  speeds  is  a  very  attractive  one,  not  lightly 
to  be  cast  aside  as  chimerical. 

The  problem  naturally  divides  itself  into  three  queries: 


FIG.  134. 

Can  it  be  done  ?  How  can  it  be  done  ?  Will  it  pay  ?  As  re- 
gards the  first  question  we  are  now  in  a  position  to  give  a 
definitely  affirmative  answer.  Suppose  we  set  for  our  goal 
a  schedule  speed  of  one  hundred  miles  per  hour.  Under 
the  conditions  which  may  be  expected  to  obtain  with  ex- 
press service,  the  corresponding  maximum  speed  would  not 
have  to  be  very  high,  probably  not  over  120  miles  per  hour. 
Obviously  the  attainment  of  such  speed  depends  on 
only  two  things — the  delivery  of  sufficient  power  to  the 
moving  locomotive,  and  the  mechanical  security  of  track 
and  rolling  stock.  In  our  present  express  service  both 


FAST   AND   HEAVY   RAILWAY  SERVICE.  275 

here  and  abroad  trains  have  within  the  past  few  years 
repeatedly  run  on  nearly  level  track  at  the  rate  of  one 
hundred  miles  per  hour  and  its  immediate  neighborhood. 
This  speed  has  not  been  maintained  for  more  than  a  few 
miles  at  a  time,  but  it  has  been  accompanied  by  no  special 
phenomena  in  the  way  of  vibration,  strain  on  track  and 
rolling  stock  or  rapid  increase  of  resistances.  In  fact  the 
motion  at  these  high  speeds  seems  to  be  smooth  and  the 
track  resistances,  if  anything,  are  less  than  at  more  mod- 
erate speeds.  Air  resistance,  once  much  dreaded,  is  not 
very  serious,  for  indicator  cards  from  locomotives  drawing 
trains  at  ninety  miles  per  hour  or  thereabouts  show  a  total 
tractive  effort  so  low  (even  below  ten  pounds  per  ton  in 
some  cases)  as  to  leave  very  little  room  for  atmospheric 
resistance. 

Perhaps  the  easiest  way  to  appreciate  the  facts  is  to 
calculate  from  the  best  attainable  data  the  power  required 
to  drive  a  given  train  at  one  hundred  miles  per  hour.  We 
shall  have  to  exterpolate  with  respect  to  some  of  our  data, 
but  so  short  a  distance  as  to  involve  very  little  uncer- 
tainty. 

The  normal  resistances  encountered  by  a  moving  train 
may  be  roughly  classified  as  friction,  grades  and  air  re- 
sistance. The  first  mentioned,  including  all  the  ordinary 
tractive  resistances,  is  usually  ten  or  twelve  pounds  per 
ton  of  moving  weight  on  good  track.  Anything  below  ten 
pounds  is  unusually  good  and  few  railway  engineers  would 
care  to  count  on  anything  below  eight  pounds  even  under 
the  most  favorable  circumstances,  although  lower  results 
are  probably  now  and  then  reached  at  high  speeds. 

The  atmospheric  resistance  used  to  be  taken  as  varying 
with  the  square  of  the  speed,  but  the  work  of  Crosby  and 
recent  experiments  with  fast  running  trains  have  made  it 
certain  that  up  to  speeds  of  fully  125  miles  per  hour  the 
air  resistance  increases  very  little  faster  than  the  speed. 
Moreover  it  can  be  greatly  lessened  by  shaping  the  front  of 
the  locomotive  into  a  plane  or  parabolic  wedge.  Fig.  135 
shows  the  results  of  Crosby's  experiments  with  whirling 


276    POWER   DISTRIBUTION   FOR   ELECTRIC  RAILROADS. 

bodies  in  addition  to  several  points  approximately  estab- 
lished by  direct  experiments  on  moving  trains.  The  latter 
are  somewhat  uncertain  owing  to  insufficient  data  concern- 
ing exposed  surfaces,  but  the  results  given  have  been 
taken  as  large  as  the  data  permit,  so  that  they  are  over 
rather  than  under  the  real  resistances. 

The  data  for  actual  train  resistances  are  in  a  very 
badly  mixed  state.  A  considerable  number  of  formulae 
have  been  deduced  from  experiments,  but  as  a  rule  they 
have  not  held  far  outside  the  experimental  limits.  Much 
of  the  confusion  has  arisen  from  trying  to  take  account  of 


40         50         60         70         80 
Miles  per  Hour 


100       110       120      130- 

Street  Ry  .Journal 


FIG.  135. 


several  complex  variables  in  one  simple  formula.  As  just 
noted,  the  air  resistance  was  at  first  assumed  to  vary  as 
the  square  of  the  speed  and  the  first  efforts  at  formulae 
assumed  a  constant  tractive  resistance  plus  a  term  includ- 
ing the  square  of  the  speed.  Now  the  law  of  squares 
assumes  in  general  terms  that  at  double  speed,  double 
the  number  of  cubic  feet  of  air  are  displaced  per  minute 
and  at  double  velocity.  Now  an  elastic  fluid  like  air, 
pushed  at  a  speed  far  below  its  velocity  for  compressional 
waves,  obeys  no  such  simple  law.  Experiments  with  pro- 
jectiles show  that  the  variation  of  resistance  with  the  ve- 
locity of  the  disturbing  body  changes  enormously  with 
that  velocity.  Of  all  the  early  workers  Rankine  alone 


FAST   AND   HEAVY   RAILWAY  SERVICE.  277 

assumed  a  term  in  the  first  power  of  the  speed  only,  quali- 
fying it  by  the  assumption  that  each  ton  of  engine  should 
be  reckoned  as  two  tons  in  computing  the  weight  of  the 
train.  A  linear  formula  substantially  takes  it  for  granted 
that  doubling  the  speed  doubles  the  air  displaced  per 
minute,  but  leaves  the  velocity  of  displacement  unchanged, 
or  that  both  quantities  are  by  no  means  doubled,  which  is 
probably  nearer  the  truth.  Crosby's  experiments  make  it 
perfectly  clear  that,  at  least  for  bodies  no  more  than  one 
or  two  diameters  long,  the  air  resistance  is  certainly  very 
close  to  a  linear  function  of  the  velocity,  and  very  far  from 
being  a  function  of  the  second  power.  For  elongated  rough 
bodies  moving  endwise,  such  as  trains,  Crosby's  values 
are  probably  somewhat  low.  Not  only  are  there  powerful 
air  eddies  at  the  rear  if  it  be  blunt,  but  there  are,  as  an  ex- 
perimental fact,  strong  inward  swirls  dragging  against  the 
train. 

In  general,  formulae  based  on  the  second  power  of  the 
speed  give  resistance  values  at  high  speeds  much  greater 
than  are  actually  found,  while  those  based  on  the  first 
power  give  two  little  resistance  at  very  low  speeds.  Those 
including  both  powers  are  more  or  less  successful  com- 
promises according  to  the  data. 

Broadly  speaking  the  facts  seem  to  be  about  as  fol- 
lows: i.  Tractive  resistances,  i.e.  journal  and  track  fric- 
tions considered  as  a  whole,  tend  to  fall  off  at  very  high 
speeds  very  possibly  showing  a  weak  maximum  at  some 
moderate  speed.  2.  Air  resistance  is  nearly  a  linear  func- 
tion of  the  speed,  with  a  slight  tendency  to  rise.  The 
combination  of  the  two  obviously  leads  to  a  shape  which 
can  be  approximated  by  either  a  parabolic  or  hyperbolic 
function  of  the  speed  in  either  case  of  small  curvature 
within  the  range  taken.  At  high  speeds  either  function 
approximates  to  a  straight  line,  while  at  low  speeds  the 
curvature  is  more  manifest. 

At  the  speeds  with  which  we  wish  here  to  deal  the 
best  available  formulae,  i.e.  those  best  confirmed  by  ex- 
periments at  very  high  speeds,  are  those  of  Mr.  Angus 


278   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

Sinclair,  Mr.  David  Barnes  and  Mr.  Vauclain,  which  are 
respectively 

R  —  2  +  .24  V 

R  — 4  +  .16  V 
R  —  3  -f  .166  V 

In  which  R  is  the  total  train  resistance  per  short  ton  and 
V  the  speed  in  miles  per  hour.  They  are  intended  for' use 
between  40  and  75  m.  p.  h. 

Fig.  136  shows  these  equations  graphically  and  with 
them  a  linear  function  based  on  Crosby's  air  resistances 


70  80 

Speed  M.P.H. 

FIG.    136. 

and  an  assumed  uniform  tractive  resistance  of  8  Ibs.  per 
ton  at  these  high  speeds,  with  the  equivalent  of  100  sq.  ft. 
of  normally  exposed  head  surface.  This  is  large  enough 
to  take  account  of  eddies  and  lateral  air  resistance.  All 
these  formulae  are  for  running  in  still  air,  and  none  of 
them  are  based  on  any  exact  theory  of  resistances,  but 
merely  fit  closely  the  facts  around  which  they  have  been 
built. 

It  should  be  distinctly  understood  that  these  formulae 
apply  to  trains  of  moderate  length  and  not  to  single  motor 
cars  such  as  have  been  used  on  electric  railways. 

The  different  values  of  the  first  term  in  the  various 


FAST  AND   HEAVY   RAILWAY  SERVICE.  279 

formulae  indicate  the  uncertainty  as  to  the  real  values  of 
the  various  forms  of  track  resistances.  If,  as  the  writer 
believes,  the  sum  of  these  gradually  rises  and  then  falls 
off  at  very  nigh  speed,  a  reason  would  appear  for  the  ap- 
parent rapid  rise  of  total  resistance  at  medium  speeds 
which  furnished  a  basis  for  the  large  terms  in  V2  in  the 
earlier  formulae  derived  for  experiments  at  moderate 
speeds.  All  the  experiments  at  60  miles  per  hour  and 
upwards  show  that  if  there  be  a  term  in  Vs  its  coefficient 
is  very  small.  It  is,  of  course,  possible  that  the  total  air 
resistance  including  eddy  effects  passes  through  a  maxi- 
mum, or  one  of  a  series  of  maxima  as  does  the  resistance 
of  a  ship,  but  only  towing  a  train  by  a  very  long  cable  is 
likely  to  bring  out  the  real  facts  of  the  case. 

For  computing  this  and  for  estimating  power  at  very 
high  speeds  it  is  best  to  recognize  squarely  the  fact  that 
one  is  dealing  with  two  distinct  classes  of  resistance,  one 
depending  011  the  weight  of  car  or  train  and  the  other  on 
head  area,  both  being  more  or  less  mixed  up  with  the 
length  and  number  of  cars.  The  process  of  calculation 
is  by  no  means  difficult  and  is  probably  more  accurate  than 
any  moderately  simple  formulae.  In  all  such  calculations 
for  high  speed  work  it  must  be  borne  in  mind  that  all  the 
facts  concerning  resistances  point  to  the  use  of  a  train 
rather  than  to  a  single  car,  driven  by  two  or  four  large 
motors  instead  of  more  smaller  ones. 

From  these  data  we  can  calculate  the  power  required 
to  drive  a  given  train  at,  say  one  hundred  miles  per  hour. 
We  will  assume  a  three-car  train,  motor  car  and  two  reg- 
ular coaches,  weighing  complete  with  passengers  140  tons. 
This  demands  no  special  construction;  in  fact  the  less 
departure  from  the  usual  form  and  appearance  of  cars  the 
better  with  respect  to  securing  traffic. 

It  is  worth  while,  however,  to  give  the  locomotive  a 
head  in  the  form  of  a  parabolic  wedge,  which  is  slightly 
better  than  the  wedge  of  Fig.  135,  to  vestibule  the  cars 
snugly,  and  to  build  the  cars  as  free  from  projection?  as  is 
consistent  with  usual  models. 


280     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

With  these  precautions  the  total  equivalent  sectional 
area  could  easily  be  kept  within  100  sq.  ft.  Nearly  all  of 
this,  too,  can  gain  advantage  from  shaping.  For  the  rela- 
tive resistance  of  wedge  and  plane  Fig.  135  gives  accurate 
values,  while  the  close  agreement  of  the  experiments  based 
on  normal  surface  attests  their  general  accuracy.  Adding 
one-third  to  the  wedge  value  for  100  miles  per  hour  to  take 
account  of  plane  and  irregular  surfaces,  we  have  a  total 
atmospheric  resistance  of  ten  pounds  per  square  foot. 

The  track  resistance  we  will  assume  at  eight  pounds  per 
ton  since  this  value  is  quite  attainable  at  high  speed  on  a 
good  track,  and  furthermore  was  used  in  computing  the 
points  shown  on  Fig.  135  so  that  if  eight  pounds  is  too  low, 
the  air  resistances  are  too  high.  We  may  now  compute  the 
total  train  resistance  as  follows: 

140   tons  at     81bs.,   ii2olbs. 
100  sq.  ft.  at  lolbs.,   1000  Ibs. 

Total  drawbar  pull,  2120  Ibs. 

At  100  miles  per  hour,  8800  ft.  per  minute,  this  means  565 
mechanical  horse  power  developed  by  the  motors.  This 
power  would  be  raised  to  about  1300  h.  p.  in  taking  a  one 
per  cent  grade  at  the  same  speed.  At  125  miles  per  hour, 
the  assumed  maximum,  the  air  resistance  would  rise  to 
about  thirteen  pounds  per  square  foot  and  the  horse  power 
to  733.  Even  if  through  increased  speed  and  headwind 
the  air  resistance  were  doubled,  the  necessary  output 
would  still-  be  below  1000  h.  p.  We  may  safely  assume 
that  with  a  nearly  level  track,  1000  h.  p.  would  suffice  for 
all  service  conditions,  while  the  normal  output  would  be 
between  500  h.  p.  and  600  h.  p. 

Now  this  output  can  readily  be  reached  with  a  power- 
ful locomotive,  and  except  for  the  difficulties  of  firing,  the 
speed  mentioned  could  be  maintained  by  a  locomotive  with 
a  single  car.  The  advantage  of  electricity  lies  with  the 
removal  of  this  difficulty  and  decrease  of  useless  weight, 
together  with  what  advantage  can  be  gained  from  a  very 
large  and  perfect  power  plant.  That  such  an  output  can 


FAST  AND   HEAVY   RAILWAY  SERVICE.  28 1 

easily  be  reached  by  motors  on  the  motor  car  admits  of  no 
question,  since  it  has  already  been  done  by  the  Baltimore 
&  Ohio  tunnel  locomotives  under  more  trying  conditions, 
i.  e. ,  moderate  speed  and  enormously  heavier  trains,  thus 
robbing  the  motors  of  the  advantage  of  high  rotative  speed. 

As  regards  track,  the  best  is  required  and  the  curves 
should  be  very  moderate,  not  less,  perhaps,  than  2000  ft. 
radius.  But  the  speeds  in  question  are  quite  feasible  on  a 
well  laid  and  well  ballasted  track.  Dr.  P.  H.  Dudley,  prob- 
ably the  greatest  living  authority  on  track,  designed  sev- 
eral years  ago  a  105  Ib.  rail  section  which  he  considered 
would  give  a  perfectly  safe  track  for  speeds  as  high  as  120 
miles  per  hour,  and  his  dynagraph  records  show,  moreover, 
that  for  such  a  track  there  is  a  marked  saving  in  power 
owing  to  much  smaller  deflections  of  the  rails.  A  140  ton 
electric  train  would  give  much  less  strain  on  the  track  than 
is  now  found  in  the  case  of  fast  express  trains  of  approx- 
imately double  that  weight. 

Nor  is  the  driving  wheel  speed  dangerously  high0 
With  good  steel  wheels  the  assumed  speed  would  have  to  be 
doubled  before  the  factor  of  safety  would  be  seriously  re- 
duced. 

Altogether,  the  evidence  shows  that  a  schedule  speed 
of  one  hundred  miles  per  hour  is  quite  possible  without 
calling  for  extraordinary  power,  unusual  material  of  con- 
struction or  great  innovations  of  any  kind. 

As  to  methods,  divers  are  available.  Ordinary  con- 
tinuous current  motors  worked  at,  say,  icooto  1500  volts 
are  competent  to  do  the  work,  but  to  facilitate  distribution 
and  keep  down  the  working  current,  alternating  motors  are 
desirable,  monophase  preferred  if  practicable.  With 
polyphase  motors  the  work  is  not  now  difficult.  The  syn- 
chronous motor  with  special  means  for  starting  is  the  neat- 
est if  stops  are  very  few,  but  is  impracticable  for  heavy 
work  of  acceleration.  For  the  high  rotative  speed  re- 
quired it  is  not  difficult  to  design  induction  motors  with 
both  high  power  factor  and  great  efficiency,  amply  capable 
of  doing  the  work  and  doing  it  well.  Probably  such  motors 


282    POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

offer  on  the  whole  the  best  available  means  for  attaining- 
the  end  in  view.  Four  motors  of  1 50  nominal  horse  power 
each,  capable  of  working  up  to  250  h.  p.  without  much  drop 
in  speed  would  be  fully  equal  to  the  work,  and  such  motors 
can  be  readily  produced  at  any  time,  as  the  size  is  nothing 
unusual,  and  the  conditions  quite  easy  to  meet.  The  work- 
ing voltage  should,  of  course,  be  kept  high;  2500  volts  is 
entirely  practical,  and  this  pressure  would  keep  the  cur- 
rent through  the  trolley  contacts  down  to  limits  already 
passed  in  present  practice.  It  is  at  least  an  open  question 
whether  under  the  conditions  which  would  be  found  on  a 
high  speed  road  of  this  kind  it  would  not  be  feasible  and 
advisable  to  use  the  whole  voltage  of  transmission — 10,000 
volts  or  more — on  the  trolley  wire  and  carry  the  trans- 
formers upon  the  locomotive.  A  bare  wire  would  be  used 
for  the  transmission  in  any  event  and  there  is  no  conclu- 
sive reason  why  it  should  not  be  carried  over  the  track. 
Otherwise  a  large  number  of  large  transformers,  aggregat- 
ing several  times  the  capacity  of  the  motors,  would  have  to 
be  distributed  along  the  line.  Unless  the  service  is  very 
heavy  this  is  needlessly  expensive  and  increases  the  items  of 
labor  and  depreciation.  Except  for  the  added  weight  and 
complication  a  rotary  transformer  on  the  car,  with  contin- 
uous current  motors,  would  prove  a  very  practicable 
method,  as  has  been  more  than  once  suggested. 

Of  course,  it  might  be  desirable  to  use  two  motors  in- 
stead of  four  and  to  vary  the  arrangement  of  parts  in  many 
ways,  but  such  details  have  no  place  here,  where  merely 
the  general  scheme  is  under  discussion. 

The  problem  of  effective  braking  is  a  serious  one,  but 
not  so  serious  as  at  first  appears.  A  well  protected  clear 
right  of  way  with  no  grade  crossings  is  absolutely  necessary 
for  speeds  like  those  considered,  and  ought  to  be  insisted 
on  even  for  present  express  speeds.  With  such  a  clear 
track  and  reduced  speed,  really  running  on  momentum,  in 
nearing  termini,  the  braking  effort  required  is  by  no 
means  out  of  reach.  The  momentum  of  a  140  ton  train 
at  ,100  miles  per  hour  is  less  than  that  of  a  300  ton  train 


FAST   AND   HEAVY   RAILWAY  SERVICE.  283 

at  60  miles  per  hour  and  about  the  same  as  that  of  a  300 
ton  train  at  50  miles  per  hour,  and  such  trains  are  within 
the  limits  of  present  practice.  To  be  sure,  the  number  of 
wheels  subject  to  braking  would  be  much  less  in  the  elec- 
tric train,  but  on  the  other  hand  a  powerful  braking  action 
can  be  obtained  by  throwing  the  motors  into  action  as 
dynamos  through  a  resistance. 

It  is  not  difficult  to  figure  the  braking  action.  Assum- 
ing, from  one  hundred  miles  per  hour  to  rest,  a  coefficient 
of  friction  of  o.  i  between  brake  shoe  and  wheels,  and  a 
brake  pressure  of  5000  Ibs.  per  wheel,  we  have  for  twenty 
wheels,  eight  on  motor  car  and  twelve  on  trail  car,  a  net 
average  retarding  effort  of  o.  i  X  5°°°  X  20  =  10,000  Ibs. 

The  air  resistance  would  average  from  our  previous 
computation  500  Ibs.,  and  at  least  2000  Ibs.  could  be 
counted  on  from  the  motors.  The  total  retarding  force 
would  then  be  10,000  +  500  +  2000  Ibs.  =  12, 500  Ibs. 
The  momentum  of  the  train  at  one  hundred  miles  per  hour 
would  be  absorbed  by  this  retardation  in  about  2500  yds. 
As  a  matter  of  fact  140  tons  is  needlessly  heavy  for  a  two- 
car  train,  and  eventually  high  speed  structures  would  be 
built  much  lighter  than  this.  It  is,  however,  perfectly  pos- 
sible to  get  the  speed  without  departing  from  ordinary  rail- 
way construction  and  the  average  man  at  present  prefers 
this  to  being  enclosed  in  the  species  of  sheet  steel  projectile 
that  has  been  thought  necessary  in  many  projects  for  high 
speed  service. 

We  may  now  take  up  the  line  question.  The  simplest 
method  is  to  make  the  working  conductor  the  transmission 
line,  as  previously  suggested.  For  the  working  condi- 
tions, monophase  transmission  gives  quite  as  great  econ- 
omy as  polyphase,  for  the  immense  conductivity  of  the 
track  gives  nearly  the  equivalent  of  a  perfectly  grounded 
circuit.  This  statement  holds  approximately  even  if  the 
conductivity  is  taken  for  alternating  currents.  The  cross 
section  of  a  pair  of  100  Ib.  rails  is,  roughly,  20  sq.  ins. 
which  leaves  an  ample  margin  even  with  the  necessary 
reduction. 


284     POWER    DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 


us  assume  a  line  one  hundred  miles  long  con- 
necting two  cities,  and  six  trains  in  regular  service. 
Using  transformers  on  the  motor  cars  the  whole  trans- 
mission problem  works  out  in  a  singularly  simple  manner. 
Using  12  as  our  track  constant  and  taking  10,000  volts 
as  terminal  voltage  with  2000  volts  extreme  drop,  a 
single  power  station  in  the  middle  of  the  line  would  do 
the  work  very  easily.  Applying  our  usual  formula  for 
1000  k.  w.  delivered 

12  X  100  X  26s,  ooo 
c.  m.  =  -  -  =  159,000. 

2OOO 

Hence  a  No.  ooo  wire  over  each  track  would  do  the  work 
easily  with  not  more  than  7^  per  cent  average  drop.  The 
total  amount  of  copper  would  then  be  about  270  tons,  cost- 
ing, say,  $75,000.  The  transformer  capacity  should  beat  a 
maximum  about  1000  k.  w.  per  train,  normally  not  over 
800  k.  w.  This  would  add  a  weight  of  not  over  eight  to 
ten  tons,  which  can  easily  be  spared  from  the  140  allowed 
for. 

The  copper  for  a  polyphase  system  would  probably  be 
in  excess  of  that  just  figured,  but  would  not  vary  materi- 
ally for  the  purpose  in  hand. 

If  the  distribution  were  effected  by  delivering  power 
to  transformers  along  the  line  the  cost  of  the  conducting 
system  would  evidently  be  much  increased,  for  the  primary 
feeding  line  could  not  be  decreased  while  retaining  the  same 
loss  and  the  secondary  working  line  would  have  to  be  of  at 
least  the  same  size  to  carry  the  necessary  working  current. 
For  the  same  total  loss  the  cost  of  copper  would  be  more 
than  doubled,  and  the  transformer  capacity  when  distrib- 
uted along  the  line  would  also  have  to  be  nearly  or  quite 
doubled.  In  point  of  total  cost  there  is  no  comparison  be- 
tween the  systems,  and  it  is  likely  that  the  maintenance 
of  the  former  would  also  be  consfderably  less,  thus  giving  a 
double  advantage.  Speaking  broadly,  one  may  at  the 
present  time  say  with  certainty,  that  a  maintained  speed  of 


FAST   AND   HEAVY   RAILWAY  SERVICE.  285 

one  hundred  miles  per  hour  is  perfectly  feasible  as  a  matter 
of  engineering.  It  requires  no  methods  that  are  really  un- 
tried, no  apparatus  that  could  not  now  be  furnished  by 
more  than  one  manufacturer  and  no  precautions  that  have 
not  already  been  taken  in  the  best  steam  railway  practice. 
When  there  is  a  demand  for  such  speed,  that  demand 
can  be  promptly  met,  be  it  for  a  road  100  or  1000  miles 
long. 

Increased  length  would  simply  mean  a  power  station 
every  hundred  miles  or  so. 

Now  as  to  the  financial  side  of  such  an  undertaking. 
It  has  been  very  judiciously  pointed  out  by  Dr.  Louis 
Duncan  in  dealing  with  the .  general  question  of  utilizing 
electricity  upon  railroads  that  no  existing  road  having  less 
than  four  tracks  could  well  undertake  to  operate  an  elec- 
tric express  system,  since  two  tracks  must  be  reserved  for 
local  and  freight  service.  While  a  local  electric  service 
and  express  service  might  be  worked  on  two  tracks  the 
general  traffic  of  a  system  would  require  more  accommoda- 
tion. The  time  is  not  yet  ripe  for  accomplishing  all  rail- 
way service  electrically,  although  there  are  forerunning 
shadows  of  such  a  probability. 

For  special  high  speed  service,  however,  there  is  ample 
opportunity  now.  A  road  between  two  considerable 
centres  of  population  with  a  schedule  speed  of  one  hundred 
miles  per  hour,  would  in  a  very  short  time  either  drive 
competing  roads  out  of  the  through  traffic  or  force  them 
to  the  same  methods.  The  longer  the  distance  the  more 
deadly  would  be  the  competition  of  fast  service.  Such 
speed  would  gather  to  itself  much  of  the  traffic  if  the  ter- 
mini were  but  a  hundred  miles  apart,  but  on  a  run  like 
that  between  New  York  and  Chicago  it  would  almost 
monopolize  it. 

In  any  given  case  the  probability  of  financial  success 
would  turn  on  the  amount  of  passenger  and  express 
traffic  between  the  points  concerned.  The  mere  motive 
power  expen.se  of  the  high  speed  is  not  serious,  nor  are 
the  items  of  repair  and  depreciation  greatly  to  be  feared. 


286     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

Assuming  an  average  output  per  train  of  600  to  650  k.  w. 
and  a  cost  of  power  at  the  station  of  about  1.25  cents  per 
kilowatt  hour,  which  should  be  quite  attainable  in  a  station 
of  4000  to  5000  k.  w.  capacity,  the  energy  itself  should 
not  cost  above  eight  cents  per  train  mile  including  all 
station  charges.  Repairs  and  depreciation  on  line,  motors 
and  rolling  stock,  and  labor  on  trains  should  not  more 
than  double  this  figure,  so  that  fifteen  to  sixteen  cents  per 
train  mile  should  cover  the  regular  charges  aside  from  ad- 
ministrative expense.  As  regards  cost  of  roadbed,  it 
varies  so  with  conditions  as  to  amount  of  grading,  number 
of  crossings,  cost  of  labor  and  so  forth,  as  to  defy  close  es- 
timation. The  rails  should  not  be  lighter  than  ninety  to  one 
hundred  pounds  per  yard,  preferably  the  latter,  and  would 
cost  $10,000  to  $12,000  per  mile  of  double  track.  The 
overhead  electric  structure,  including  the  copper  for  high 
tension  current  and  the  track  connections,  should  not  cost 
more  than  $3000  per  mile.  The  station  complete  with  steam 
plant  and  all  necessary  electrical  apparatus  could  be  in- 
stalled ready  for  running  for  $350,000 to $400,000,  perhaps 
less,  for  one  hundred  miles  of  road.  The  total  cost  would 
thus  be  for  such  a  section  probably  not  over  $15,000  per 
mile,  plus  right  of  way  and  general  construction  of  road- 
bed, etc. 

The  total  cost  would  thus  be  not  much  in  excess  of 
that  of  a  first  class  steam  road  in  the  same  situation,  and 
with  the  volume  of  first  class  passenger,  mail,  special 
freight  and  express  service  to  be  expected  between  two  im- 
portant termini,  it  would  nearly  always  pay  if  built  for  cash 
and  operated  for  profit. 

For  elevated  roads  electric  traction  cannot  be  in  the 
future  treated  as  a  luxury,  but  it  must  be  considered  a  ne- 
cessity. Even  were  it  notably  more  costly  than  traction  by 
steam  locomotives,  instead  of  the  reverse,  public  opinion 
from  now  on  will  compel  its  use  in  every  new  enterprise, 
and  on  existing  roads  will  make  abolition  of  the  locomo- 
tive the  price  of  the  slightest  municipal  concession. 

Aside  from  this  consideration  the  experience  with  the 


FAST   AND   HEAVY   RAILWAY  SERVICE}. 


287 


Intramural  line  during  the  World's  Fair,  and  subsequent 
results  on  the  Metropolitan  &  Lake  Street  elevated  roads 
in  Chicago  and  several  others,  have  shown,  what  theoretical 
investigation  had  indicated,  that  for  such  service  electric 
power  is  the  cheapest  available  means  of  propulsion. 

Elevated  service  is  of  a  rather  trying  nature  on  account 
of  the  frequent  stops — generally  about  every  quarter  of  a 
mik — and  the  large  amount  of  power  that  has  to  be  used 


MAP  OF 

THE  METROPOLITAN 

WEST  SIDE  ELEVATED  R.  R. 

Chicago,  Illinois 


Street  Ry  Journal 


in  acceleration.  The  experiments  of  Mr.  Sprague  made  on 
the  Third  Avenue  elevated  road  in  New  York  established 
the  facts  very  clearly.  It  was  found  that  for  the  ordinary 
train,  weighing  from  eighty  to  ninety  tons,  with  a  speed 
reaching,  between  stations,  twenty  to  twenty-five  miles  per 
hour,  the  average  indicated  horse  power  of  the  locomotives 
during  service  was  70.3  reaching  an  occasional  maximum 
of  185.  These  great  inequalities  almost  vanished  when  the 
whole  power  for  the  line  was  considered.  Sixty-three 
trains  were  in  ordinary  use  and  the  mean  power,  smoothed 
out  by  the  large  number  of  units,  varied  little  from  4500  in- 


288     POWER   DISTRIBUTION   FOR   EXECTRIC   RAILROADS. 

dicated   horse  power.     The  coal  used   on  the   locomotives 
amounted  to  6.2  Ibs.  per  horse  power  hour  while  in  use. 

With  these  facts  as  to  power  required  the  electrical 
conditions  are  easy  to  find.  The  motors  should  together  be 
able  to  work  readily  up  to  200  h.p.  with  a  good  efficiency 
at  half  this  output.  The  average  power  required  is  not 
far  from  that  already  computed  for  the  case  of  suburban 
service  at  higher  speed  and  with  rather  lighter  trains. 

The  load,  however,  is  on  the  whole  more  uniform  on 
the  elevated  line,  although  varying  more  as  regards  indi- 
vidual units.  The  cost  of  power  should  therefore  be 
somewhat  less. 

The  first  notable  electric  elevated  road  in  service  in 
this  country  was  the  Metropolitan  line  in  Chicago.  This 
road,  which  went  into  operation  in  the  spring  of  1895,  was 
designed  to  furnish  rapid  transit  on  the  west  side  of  Chi- 
cago. Its  general  location  is  well  shown  on  the  map 
(Fig.  137). 

The  portion  now  in  operation  consists  of  1 3  ^  miles  of 
double  track  with  thirty-two  stations.  The  structure  is  a 
substantial  one  of  deep  plate  girders,  admirable  mechanic- 
ally, but  very  unsightly.  The  track  is  of  ninety  pound  rail 
with  massive  guard  timbers. 

The  electrical  equipment,  with  which  only  we  are  here 
concerned,  involved  divers  excellent  and  novel  features.  In 
the  first  place  the  track  rails  are  not  bonded  together  in 
the  usual  way,  but  each  rail  is  bonded  in  the  middle  to  the 
supporting  structure,  thus  giving  an  enormous  iron  con- 
ductor for  the  return  circuit.  If  thoroughly  carried  out 
this  arrangement  is  exceedingly  effective,  although  it 
would  be  well  to  bond  the  track  itself  as  a  precaution 
against  bad  bonds  in  occasional  rails. 

The  working  current  is  taken  from  a  contact  rail  lo- 
cated a  few  inches  outside  of  and  above  the  track  rail. 
This  contact  rail  is  supported  about  every  six  feet  by  blocks 
of  paraffine-soaked  wood  to  which  it  is  secured  by  clips  held 
in  place  by  wood  screws.  This  rail  weighs  forty-five 
pounds  per  yard  and  the  insulated  blocks  are  six  inches 


FAST   ANI>   HEAVY   RAILWAY   SERVICE.  289 

square  and  rest  upon  iron  brackets  about  one  inch  high, 
thus  raising  the  contact  rail  about  seven  inches  above  the 
general  level  of  the  track  rails. 

A  rail  joint  in  position  is  shown  in  Fig.  138.     At  the 


FIG.  13?. 

joint  the  rails  are  held  in  line  by  a  light  fishplate  secured 
by  two  bolts,  and  are  thoroughly  bonded.  The  bonds  are 
formed  of  flexible  copper  strip  about  -fy  in.  thick  and  the 
full  width  of  the  foot  of  the  rail,  under  which  they  are 


FIG.  139. 

placed  and  to  which  .they  are  secured  by  two  large  rivets, 
one  on  each  side  of  the  web  of  each  rail. 

Current  is  taken  off  this  contact  rail  by  chilled  cast 
iron  shoes  carried  on  the  trucks.  One  of  these  is  shown 
ira  Fig.  139,  which  exhibits  the  arrangement  of  its  parts  and 


290     POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS 

the  connecting  cable.  The  general  construction  is  that  of 
a  double  toggle,  and  the  weight  of  the  shoe  is  sufficient  to 
ensure  contact,  no  spring  being  employed.  There  are 
four  of  these  contact  shoes  on  each  motor  car,  one  at  each 
corner.  All  are  ready  for  service.  Two  are  normally  in 
contact  with  the  feed  rail,  and  when,  as  at  some  switches, 
it  is  desirable  for  this  rail  to  change  sides,  the  correspond- 
ing shoes  go  into  service.  The  device  works  admirably. 

The  feeding  system  is  extraordinary.  It  is  composed 
of  forty-five  pound  steel  rails,  like  the  contact  rail,  sup- 
ported on  and  insulated  from  the  main  structure  and  boxed 
with  boards  to  keep  them  out  of  mischief.  These  rails  are 
thoroughly  bonded,  cross  bonded  when  feasible,  and  are 
connected  to  the  supply  rail  about  every  300  ft. ,  of tener  at 
switches  and  sidings. 

On  the  section  from  the  power  house  to  the  eastern 
terminus,  about  i  ^  miles,  the  contact  rails  alone  are  suf- 
ficient, but  westward  from  the  power  house  run  eighteen 
feeder  rails,  supplying  various  sections  of  the  road,  and 
each  connected  to  the  distribution  board  in  the  power 
house.  On  the  eastern  section  current  is  taken  under 
the  Chicago  River  by  lead  covered  cables  laid  in  a  trench 
dredged  in  the  mud  bottom.  There  are  eighteen  of  these 
cables,  four  of  500,000  c.  m.  each,  the  others  of  235,000. 
c.  m. 

The  motor  cars  are  forty- eight  feet  long  and,  except 
for  a  steel  sub-frame  for  extra  strength,  display  no  re- 
markable peculiarities.  Each  is  equipped  with  two  G.  E. 
2000  motors,  like  those  shown  in  connection  with  the  Nan- 
tasket  road.  At  each  end  of  the  car,  occupying  half  its 
width  and  projecting  into  the  car  and  onto  the  platform, 
is  a  little  cab  containing  the  controlling  apparatus,  auto- 
matic motor  pump  for  the  air  brakes,  and  other  acces- 
sories. The  motor  car  complete  weighs  about  twenty-five 
tons.  The  operation  of  the  whole  system  has  been  highly 
successful. 

The  Lake  Street  elevated  road,  equipped  about  a  year 
later, shows  some  useful  modifications,  although  the  general 


FAST  AND   HEAVY   RAILWAY  SERVICE. 


29I 


equipment  is  much  the  same.  The  working  conductor 
is  here  a  forty-eight  pound  T  rail,  located  much  as  in  the 
Metropolitan  line,  but  supported  on  special  insulators  in- 
stead of  wooden  blocks.  These  insulators  have  a  cast  iron 
base  and  clamping  top,  united  by  a  bolt  sheathed  like  a 


Street  Ry.Journal 


FIG.  140. 


trolley  hanger  in  dense  insulation.  This  bolt  is  screwed 
into  the  base  and  secured  to  the  cap  by  a  coarse  thread 
cast  in  cap  and  insulation  and  packed  with  melted  sulphur. 
Fig.  140  shows  the  arrangement  of  this  standard  with  its 
rail  and  guard  planks.  These  insulating  chairs  support 
the  rail  every  six  feet.  The  bonding  of  the  third  rail  is 
with  copper  strips,  secured  to  the  rail  with  two  rivets, 
Y^  in.  in  diameter,  while  the  track  rails  are  bonded  to  the 
main  structure  at  their  middle  points. 


2Q2     POWER   DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 

The  feeders  on  this  road  are  of  copper  cable,  bare  on 
the  structure,  but  boxed  over.  They  are  supported  every 
ten  feet  by  vitrified  clay  insulators  arranged  as  shown  in 
Fig.  141.  Every  hundred  feet  this  clay  insulator  is  re- 
placed by  an  iron  clamp  provided  with  insulating  bushing, 
The  cables  are  of  1,000,000  and  1,500,000  c.  m.  section. 

The  contact  rail  is  well  guarded,  in  this  construction, 
a  precaution  that  should  be  carried  out  on  every  such  road 
and  particularly  when  a  contact  rail  is  used  as  at  Nan- 


iron  supports  100  ft.  centers    * 
FIG.    141. 

tasket  for  a  surface  road.  The  earliest  elevated  road  in 
Chicago,  the  so-called  "  Alley"  line  has  been  equipped 
for  electric  traction  and  the  New  York  elevated  roads  are 
now  taking  a  similar  step. 

It  is  highly_probable  that  copper  feeders  are  in  the 
long  run  more  economical  than  feeders  composed  of  rails. 
When  freshly  bonded  the  rail  feeders  just  described  had 
about  one-tenth  the  net  conductivity  of  the  same  weight 
of  copper.  At  present  prices  of  new  rails  and  copper  the 
total  cost  of  the  feeding  system  is  about  the  same  by 
either  method,  with  the  maintenance  and  depreciation 


FAST  AND   HEAVY   RAILWAY  SERVICE.  293 

greatly  in  favor  of  the  copper.  Even  if  old  worn  out  rails 
were  utilized  for  the  feeders  it  is  an  open  question  whether 
the  extra  maintenance  would  not  eventually  more  than  eat 
up  the  saving  in  first  cost  over  copper. 

Personally  the  author  believes  the  centre  rail  con- 
struction used  at  Nantasket  to  be  better  than  any  side  rail 
for  elevated  service,  where  it  can  readily  be  given  ample 
insulation  for  all  ordinary  cases.  It  is  quite  as  easy  to 
put  in  place,  and  the  great  cross  section  of  the.  rail  is  ad- 
vantageous, since  the  bonding  must  be  maintained  in  any 
case  and  the  extra  conductivity  costs  less  than  if  it  were 
secured  by  copper  feeders. 

Whatever  the  construction,  a  third  rail  supply  system 
must  be  protected  against  danger  of  accidental  contacts, 
and  the  insulators  must  be  kept  free  of  conducting  material 
— brake  shoe  dust  and  the  like. 

On  a  large  system  the  electrical  load  is  fairly  constant 
and,  except  for  the  question  of  branches,  can  be  considered 
as  nearly  uniformly  distributed.  If  the  schedule  is  pre- 
served, there  is  unlikely  to  be  any  very  great  massing  of 
cars,  so  that  less  provision  has  to  be  made  for  wandering  of 
the  load  than  in  street  railway  service  or  even  suburban 
service.  This  simplifies  the  computation  of  the  conducting 
system  greatly.  If  the  rails  are  thoroughly  bonded  to  the 
structure,  and  preferably  also  to  each  other,  the  resistance 
of  the  return  circuit  is  extremely  low.  A  track  constant 
of  1 2  should  be  quite  enough  to  allow  under  these  circum- 
stances, and  the  power  demanded  should  not  often  average 
over  seventy-five  kilowatts  per  train  at  the  power  house. 
The  work  of  rapid  acceleration  is  the  most  severe  contin- 
gency that  must  be  taken  into  account,  for  elevated  roads 
are  practically  level.  This  work  will  usually  be  not  far 
from  double  the  average  work,  at  times  perhaps  consid- 
erably more. 

An  elevated  structure  gives  an  admirable  opportunity 
for  the  use  of  polyphase  motors,  since  the  three  necessary 
working  conductors  can  readily  be  provided,  and  such  a 
system  has  been  several  times  suggested.  In  long  roads 
an  alternating  distribution  at  high  voltage  might  be 


294   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 


advantageous,  but  intrinsically,  under  the  necessary  con- 
ditions of  frequent  stopping  and  starting,  heavy  loads  of 
acceleration  and  large  power  units,  there  is  very  small 
reason  for  abandoning  the  continuous  current  motor.  If 
the  conditions  of  distribution  demand  high  voltage  feeders, 
however,  a  polyphase  motor  system  can  be  made  to  meet 
fully  the  conditions  of  service. 

Aside  from  elevated  service  the  most  promising  field 
for  heavy  electric  traction  is  in  those  special  cases  where 


FIG.  142. 

the  abolition  of  the  steam  locomotive  is  in  itself  desirable 
quite  apart  from  the  question  of  saving.  Such  cases  are 
plentiful  enough,  particularly  in  tunnels  and  large  terminal 
work  in  cities.  The  time  is  near  when  cities  will  defend 
themselves  by  legislative  enactment  against  the  well  nigh 
intolerable  nuisance  of  scores  of  smoking  locomotives, 
polluting  the  air  and  distributing  cinders  with  lavish  pro- 
fusion. While  there  was  no  practical  means  of  avoiding  the 
trouble  it  was  endured,  but  with  the  means  at  hand  the 
people  are  likely  at  any  time  to  "  get  up  and  biff  you/'  as 
the  phenomenon  was  happily  described  by  a  certain  distin- 
guished politician  lately  released  from  the  penitentiary. 


FAST  AND   HEAVY   RAILWAY  SERVICE. 


295 


Terminal  yards  in  the  heart  of  a  city  are  as  at  present 
operated  simply  an  abominable  nuisance.  Tunnels  in  ad- 
dition are  often  more  or  less  dangerous.  Any  one  who 
has  been  through  the  St.  Louis  tunnel  or  the  St.  Clair 
tunnel  at  Port  Huron  realizes  that  stalling  a  train  would 
be  a  very  serious  matter,  with  an  unpleasantly  good 
chance  for  asphyxiation.  Ventilation  is  at  best  difficult 
and  seldom  well  done. 

The  now  notable  experiment  of  the  Baltimore  &  Ohio 
Railroad  in  escaping  from  the  tunnel  difficulty  has  proved 


FIG.    14;. 

so  successful  as  to  leave  no  doubts  as  to  the  applicability  of 
electric  traction  to  this  and  all  similar  work. 

This  tunnel  runs  through  the  heart  of  the  city  of  Bal- 
timore. It  is  7350  ft.  long,  27  ft.  maximum  width  and  22 
ft.  maximum  height.  Its  relation  to  the  transit  through 
Baltimore  is  well  shown  in  Fig.  142.  The  old  route  via  the 
ferry  caused  continual  delays  and  annoyance  and  was  a 
constant  stumbling  block  in  the  way  of  a  fast  through  serv- 
ice to  Washington.  The  completion  of  the  tunnel  has 
saved  nearly  twenty  minutes  in  the  time  between  New 


296     POWER    DISTRIBUTION    FOR    ELECTRIC   RAILROADS. 

York  and  Washington,  besides  facilitating  the  general  serv- 
ice greatly.  Unfortunately  it  was  necessary  to  have  a  grade 
of  nearly  forty-three  feet  to  the  mile  in  the  main  tunnel, 
and  this  demanded  so  great  power  in  hauling  the  heavy 
freight  service  as  to  make  the  smoke  question  exceedingly 
grave.  In  attempting  to  carry  it  on  by  steam  locomotives 
just  after  the  completion  of  the  tunnel  several  men  were 
asphyxiated,  and  freight  service  via  the  tunnel  was  dropped 
until  the  electric  equipment  was  ready.  The  relatively 
light  passenger  service  caused  comparatively  little  trouble 
from  smoke. 

The  first  electric  locomotive  went  into  regular  sendee 


FIG.  144. 

on  Aug.  4,  1895,  and  has  operated  with  entire  success 
since  that  date.  The  total  length  of  the  electric  run,  in- 
cluding the  approaches  to  the  tunnel,  is  about  two  miles. 

The  locomotive  complete  is  shown  in  Fig.  143.  It  is  of 
standard  gauge,  35  ft.  long  and  9  ft.  6%  ins.  extreme 
width,  and  weighs  complete  96  tons.  It  is  composed  of 
two  flexibly  connected  trucks,  each  having  four  driving 
wheels  62  ins.  in  diameter  on  a  6  ft.  10  in.  wheel  base. 
All  the  weight  is,  of  course,  on  the  drivers. 

On  each  of  the  four  driving  axles  is  mounted  a  six- 
pole,  direct  connected  motor  of  360  nominal  horse  power. 
These  motors,  shown  unassembled  in  Fig.  144,  are  not 
placed  directly  upon  the  axle.  The  armature  shaft  is  a 
sleeve  thirteen  inches  in  exterior  diameter,  concentric  with 


FAST   AND   HEAVY   RAILWAY   SERVICE. 


297 


the  axle,  but  with  a  clearance  of  about  i  ^  ins.  On  this 
armature  shaft  is  carried  a  five-armed  driving  spider  which 
bears  on  lugs  on  the  driving  wheels  through  intermediary 
rubber  cushions.  The  axle  is  thus  relieved  of  the  direct 
weight  of  the  armature  and  there  is  sufficient  flexibility  to 
take  up  vibration  due  to  irregularities  of  track.  The  loco- 
motive is  fitted  with  air  brakes  and  air  whistle,  and  a 
headlight  at  each  end. 

The  supply  of  the  immense  current  demanded  by  such 
a  locomotive  at   full  load  was  a  difficult   matter  and  the 


FIG.  145. 

need  was  met  by  a  most  ingenious  and  effective,  though 
from  our  present  point  of  view  too  complicated  and  costly, 
arrangement.  This  was  a  species  of  reversion  to  the  slotted 
tube  used  on  some  of  the  earliest  foreign  electric  roads, 
from  which  current  was  taken  by  an  interior  brush  some- 
thing like  a  gun  cleaner.  In  this  case,  however,  the  tube 
was  built  up  of  two  angle  irons  bolted  to  a  covering  strip 
and  weighing  about  ninety  pounds  per  yard.  The  channels 
thus  formed  are  carried  on  trusses  in  the  open  and  sus- 
pended from  the  arch  within  the  tunnel.  Fig.  146  shows 
the  character  of  the  hollow  working  conductor  and  the 


-         , 

UNIVERSITY 


POWER   DISTRIBUTION    FOR    ELECTRIC    RAILROADS. 


method  of  supporting  it  in  the  tunnel.  Current  is  taken 
off  by  a  snug-fitting  brass  shuttle  carried  on  a  toggle  joint 
trolley  frame,  and  leading  to  the  motors  by  a  flexible  cable. 
Fig.  136  gives  a  clear  idea  of  this  trolley  structure,  which  in 
practice  does  its  work  exceedingly  well.  Save  for  occa- 
sional trouble  before  the  conductors  were  cleared  of  rust 
and  dirt,  at  the  verv  first,  the  arrangement  has  left  little 
to  be  desired.  The  conductor  in  the  tunnel  is  supported 
every  fifteen  feet,  and  outside  the  tunnel  the  spans  are  thirty 
to  sixty  feet.  The  trolley  support  has  great  lateral  flexi- 
bility and  the  working  conductor  is  normally  alongside  the 
locomotive  rather  than  over  it. 


FIG.  146. 

The  power  house  is  near  the  southern  terminus  of  the 
electric  system  and  current  is  taken  from  it  to  various 
points  on  the  line  over  1,000,000  c.  m.  feeder  cables.  The 
working  conductor  is  carefully  bonded  at  each  joint  by  two 
No.  oooo  bond  wires. 

Now  as  to  operation.  After  continuous  service  for 
more  than  four  years,  the  system  has  shown  itself  to  be 
thoroughly  efficient  and  reliable.  Repairs  have  been  light, 
the  working  conductors  have  been  easily  kept  clean  by 
running  through  a  scraping  shoe  every  two  or  three  weeks, 
the  leakage  current  in  spite  of  the  moisture  of  parts  of  the 
tunnel  and  very  dirty  insulators  has  been  only  about 
four  amperes. 


FAST   AND   HKAVY   RAILWAY   SERVICE, 


299 


In  a  sample  month  of  operation,  locomotive  No.  I 
ran  5168  miles  in  regular  service,  hauled  through  the 
tunnel  375,000  tons  in  trains  averaging  a  little  over  1000 
tons  apiece,  and  did  this  at  a  total  cost  for  labor,  fuel, 
maintenance  and  incidentals,  of  $2186. 

This  means  a  cost  of  0.58  cent  per  ton  actually  hauled, 
or  42. 3  cent0  per  engine  mile.  But  with  the  three  locomo- 
tives now  in  service,  the  labor  expense  at  the  power  house 
is  unincreased,  while  the  other  expenses  increase  with  the 


Seconds 
FIG.    147. 

number  of  locomotives  in  service.  The  result  is  greatly  to 
reduce  the  cost  per  engine  mile,  probably  to  between 
twenty-five  and  thirty  cents.  The  cost  per  engine  mile  for 
the  freight  service  of  one  of  the  large  steam  railroad  sys- 
tems is  stated  to  be  on  the  average  26.  i  cents. ,  varying  on 
the  different  sections  between  twenty- three  and  thirty-four 
cents,  so  that  the  electric  traction  does  not  differ  notably  in 
cost  from  steam  haulage,  in  spite  of  the  fact  that  the  station 
is  necessarily  somewhat  uneconomical  from  the  frequent 
periods  of  light  load.  The  coal  consumption  during  the 


300    POWER  DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

month  in  question  was  294  tons,  which  shows  the  unfavor- 
able load  conditions  very  forcibly.  Increased  service  would 
improve  this  notably.  The  average  amperes  per  train 
during  the  same  period  were  986,  showing  an  aver- 
age input,  at  the  usual  voltage  of  625.  of  about  600 
k.  w.  With  a  500  ton  train  a  speed  of  thirty-five  to  forty 
miles  per  hour  could  be  reached,  and  on  one  occasion  a 
1900  ton  train  was  taken  through  the  tunnel  up  grade. 
The  drawbar  pull  in  this  case  reached  63,000  Ibs.  Fig.  147 
shows  the  current  required  for  acceleration  and  running 
of  a  moderate  train  (875  tons)  on  the  grade.  The  severe 
character  of  the  work  is  sufficiently  evident,  and  the  effect 
on  the  economy  of  the  power  station  of  an  intermittent  load 
of  this  kind  is  obvious.  The  plant  efficiency  with  the 
three  locomotives  is  very  materially  increased. 

These  General  Electric  Baltimore  &  Ohio  locomotives 
were  intended  for  very  heavy  service  at  moderate  speeds 
— about  thirty  miles  per  hour— but  on  a  spurt  of  the 
engine  alone  up  the  grade  more  than  double  this  has  been 
reached. 

A  radically  different  type  of  locomotive  intended  for  a 
different  class  of  service  is  the  Westinghouse-Baldwin 
machine  shown  in  Fig.  148.  It  is  built  along  the  lines  of  a 
motor  car,  and  is  in  fact  a  combined  baggage  car  and  loco- 
motive. It  is  thirty-eight  feet  long  and  eight  feet  wide 
and  weighs  complete  eighty  tons.  The  eight  forty-two- 
inch  driving  wheels  are  mounted  on  two  trucks  with  un- 
usually long  wheel  base.  On  each  axle  is  a  250  h.  p. 
geared  motor.  By  this  means  lighter  and  cheaper  motors 
can  be  used  than  with  the  direct  coupled  construction. 
The  gearing  is  arranged  for  a  full  speed  of  seventy-five 
miles  per  hour,  as  the  locomotive  is  designed  for  fast 
passenger  service.  As  in  the  Baltimore  &  Ohio  locomotives 
*he  motors  are  arranged  for  series-parallel  control. 

The  problem  of  distributing  power  to  units  of  so  great 
capacity  as  these  is  serious.  For  tunnel  work  and  perhaps 
for  general  work  on  special  tracks,  the  centre  rail  distribu- 
tion used  on  the  Nantasket  road  or  a  corresponding  side 


303   POWER   DISTRIBUTION   FOR   ELECTRIC   RAILROADS. 

rail  is  to  be  preferred  to  anything  as  yet  proposed  for 
heavy  currents.  With  very  high  voltage  the  overhead  or 
side  running  trolley  becomes  necessary  and  with  a  trolley 
wire  of  large  section  and  a  pair  of  trolleys  there  is  little 
difficulty  in  operating  locomotives  of  moderate  capacity 
even  at  600  or  700  volts.  The  enormous  capacity  of  the 
B.  &  O.  locomotives  leads  to  quite  exceptional  difficulty 
in  taking  current.  At  ordinary  voltages  the  feeder  section 
required  at  even  moderate  distances  is  formidable.  To  op- 
erate two  locomotives  of  the  B.  &  O.  pattern  on  a  two  mile 
section  with  the  power  house  at  one  terminus  requires  a 
capacity  for  delivering  the  equivalent  of  about  3000  am- 
peres at  the  end  of  the  line.  From  Plate  II,  using  16  as 
track  constant,  since  the  conductivity  of  the  track  cannot 
safely  be  taken  as  more  than  twice  that  of  the  outgoing 
system,  the  feeder  area  required  for  a  transmission  of 
10,000  ft.  at  i oo  volts  loss  is  4, 800,000  c.  m.  Using  loolb. 
center  rails  on  a  double  track  one  gets  about  2,200,000 
c.  m.  equivalent  conductivity,  leaving  2,600,000  to  be 
supplied  by  supplementary  feeders.  By  allowing  a  little 
extra  drop  this  could  safely  be  reduced  to,  say,  two  1,000,- 
ooo  c.  m.  cables. 

It  at  once  becomes  evident  that  direct  supply  at  ordi- 
nary voltages  is  out  of  the  question,  except  for  relatively 
very  short  distances.  For  more  extensive  work  we  are 
brought  back  either  to  high  voltage  supply  with  trans- 
formers and  perhaps  rotary  converters  on  the  locomotive 
or  with  a  low  voltage  working  conductor  supplied  from 
transformers  or  rotaries  along  the  track.  Direct  current 
throughout  is  barred  out  by  the  conditions  of  practical 
working  except  in  cases  similar  to  that  just  described. 

For  heavy  special  service  in  yards  and  tunnels  the  cen- 
ter rail  is  undoubtedly  the  simplest  and  most  practical 
method  of  distribution  yet  tried,  and  for  such  service  con- 
tinuous current  motors  at  600  to  1000  volts  with  series-paral- 
lel control,  leave  little  to  be  desired.  If  in  the  course  of 
development  alternating  long  distance  service  has  to  be 
linked  to  heavy  terminal  traffic,  a  terminal  power  system  at 


FAST  AND   HEAVY   RAILWAY  SERVICE.  303 

moderate  voltage  and  relatively  low  frequency  meets  the 
requirements.  The  growth  of  heavy  electric  traction  in 
the  past  few  years  has  been  in  the  direction  of  rather  long 
interurban  roads  worked  at  moderate  speeds,  and  now  and 
then  involving  freight  haulage  by  good  sized  electric  loco- 
motives. Of  such  practice  there  are  many  admirable 
instances  without  any  material  change  in  apparatus  or 
methods  of  distribution.  The  period  has  been  rich  in 
minor  improvements  and  much  experience  has  been  ac- 
quired within  a  somewhat  limited  range.  The  most  nota- 
ble item  of  growth  has  been  the  complete  demonstration 
of  the  success  of  the  slotted  conduit  system,  which  how- 
ever, is  beyond  the  scope  of  this  work  except  in  so  far  as 
it  has  been  noted  already. 

A  little  latter  a  new  period  of  activity  in  methods, 
such  as  generally  follows  a  season  of  standardization,  may 
reasonably  be  expected. 

That  fast  electric  trains  over  long  distances  are  soon 
coming,  no  one  who  is  conversant  with  the  art  of  electric 
traction  can  seriously  doubt.  How  extensive  such  service 
will  be,  how  far  it  will  supersede  present  methods,  and 
what  methods  out  of  those  which  are  now  practicable  will 
survive  competitive  trial — these  are  questions  for  the 
prophet  rather  than  the  engineer. 


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